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Abstract: A direct simulation Monte Carlo (DSMC) method is applied to model collisions between He buffer gas atoms and ammonia molecules within a buffer gas cell. State-to-state cross sections, calculated as a function of the collision energy, enable the inelastic collisions between He and NH3 to be considered explicitly. The inclusion of rotational-state-changing collisions affects the translational temperature of the beam, indicating that elastic and inelastic processes should not be considered in isolation. The properties of the cold molecular beam exiting the cell are examined as a function of the cell parameters and operating conditions; the rotational and translational energy distributions are in accord with experimental measurements. The DSMC calculations show that thermalisation occurs well within the typical 10-20 mm length of many buffer gas cells, suggesting that shorter cells could be employed in many instances - yielding a higher flux of cold molecules. © 2017 Author(s).
BibTeX:
@article{Doppelbauer2017,
  author = {Doppelbauer, M.J. and Schullian, O. and Loreau, J. and Vaeck, N. and Van Der Avoird, A. and Rennick, C.J. and Softley, T.P. and Heazlewood, B.R.},
  title = {Using a direct simulation Monte Carlo approach to model collisions in a buffer gas cell},
  journal = {Journal of Chemical Physics},
  year = {2017},
  volume = {146},
  article number = {044302},
  doi = {10.1063/1.4974253}
}
Abstract: The present work reports results from systematic multiconfiguration Dirac-Hartree-Fock calculations of electronic isotope-shift factors for a set of transitions between low-lying states in neutral zinc. These electronic quantities, together with observed isotope shifts between different pairs of isotopes, provide the changes in mean-square charge radii of the atomic nuclei. Within this computational approach, different models for electron correlation are explored in a systematic way to determine a reliable computational strategy and to estimate theoretical error bars of the isotope-shift factors. © 2017 American Physical Society.
BibTeX:
@article{Filippin2017,
  author = {Filippin, L. and Bieroń, J. and Gaigalas, G. and Godefroid, M. and Jönsson, P.},
  title = {Multiconfiguration calculations of electronic isotope-shift factors in Zn i},
  journal = {Physical Review A},
  year = {2017},
  volume = {96},
  article number = {042502},
  doi = {10.1103/PhysRevA.96.042502}
}
Abstract: Context. On 20 January 2015 the Rosetta spacecraft was at a heliocentric distance of 2.5 AU, accompanying comet 67P/Churyumov-Gerasimenko on its journey toward the Sun. The Ion Composition Analyser (RPC-ICA), other instruments of the Rosetta Plasma Consortium, and the ROSINA instrument made observations relevant to the generation of plasma waves in the cometary environment. Aims. Observations of plasma waves by the Rosetta Plasma Consortium Langmuir probe (RPC-LAP) can be explained by dispersion relations calculated based on measurements of ions by the Rosetta Plasma Consortium Ion Composition Analyser (RPC-ICA), and this gives insight into the relationship between plasma phenomena and the neutral coma, which is observed by the Comet Pressure Sensor of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis instrument (ROSINA-COPS). Methods. We use the simple pole expansion technique to compute dispersion relations for waves on ion timescales based on the observed ion distribution functions. These dispersion relations are then compared to the waves that are observed. Data from the instruments RPC-LAP, RPC-ICA and the mutual impedance probe (RPC-MIP) are compared to find the best estimate of the plasma density. Results. We find that ion acoustic waves are present in the plasma at comet 67P/Churyumov-Gerasimenko, where the major ion species is H2O+. The bulk of the ion distribution is cold, kBTi = 0.01 eV when the ion acoustic waves are observed. At times when the neutral density is high, ions are heated through acceleration by the solar wind electric field and scattered in collisions with the neutrals. This process heats the ions to about 1 eV, which leads to significant damping of the ion acoustic waves. Conclusions. In conclusion, we show that ion acoustic waves appear in the H2O+ plasmas at comet 67P/Churyumov-Gerasimenko and how the interaction between the neutral and ion populations affects the wave properties. © ESO, 2017.
BibTeX:
@article{Gunell2017,
  author = {Gunell, H. and Nilsson, H. and Hamrin, M. and Eriksson, A. and Odelstad, E. and Maggiolo, R. and Henri, P. and Vallieres, X. and Altwegg, K. and Tzou, C.-Y. and Rubin, M. and Glassmeier, K.-H. and Wieser, G.S. and Wedlund, C.S. and De Keyser, J. and Dhooghe, F. and Cessateur, G. and Gibbons, A.},
  title = {Ion acoustic waves at comet 67P/Churyumov-Gerasimenko: Observations and computations},
  journal = {Astronomy and Astrophysics},
  year = {2017},
  volume = {600},
  article number = {A3},
  doi = {10.1051/0004-6361/201629801}
}
Abstract: We have performed a systematic ab initio study on alkali and alkaline earth hydroxide neutral (MOH) and anionic (MOH-) species where M = Li, Na, K, Rb, Cs or Be, Mg, Ca, Sr, Ba. The CCSD(T) method with extended basis sets and Dirac-Fock relativistic effective core potentials for the heavier atoms has been used to study their equilibrium geometries, interaction energies, electron affinities, electric dipole moment, and potential energy surfaces. All neutral and anionic species exhibit a linear shape with the exception of BeOH, BeOH-, and MgOH-, for which the equilibrium structure is found to be bent. Our analysis shows that the alkaline earth hydroxide anions are valence-bound whereas the alkali hydroxide anions are dipole bound. In the context of sympathetic cooling of OH- by collision with ultracold alkali and alkaline earth atoms, we investigate the 2D MOH- potential energy surfaces and the associative detachment reaction M + OH→- MOH + e-, which is the only energetically allowed reactive channel in the cold regime. We discuss the implication for the sympathetic cooling of OH- and conclude that Li and K are the best candidates for an ultracold buffer gas. © 2017 Author(s).
BibTeX:
@article{Kas2017,
  author = {Kas, M. and Loreau, J. and Liévin, J. and Vaeck, N.},
  title = {Ab initio study of the neutral and anionic alkali and alkaline earth hydroxides: Electronic structure and prospects for sympathetic cooling of OH-},
  journal = {Journal of Chemical Physics},
  year = {2017},
  volume = {146},
  article number = {194309},
  doi = {10.1063/1.4983627}
}
Abstract: We present measurements of ion-pair dissociation (IPD) of highly excited neutral and ionized carbon clusters Cn=2-5(q=0-3)+. The tool for producing these species was a high-velocity collision between Cn+ projectiles (v=2.25 a.u.) and helium atoms. The setup allowed us to detect in coincidence anionic and cationic fragments, event by event, leading to a direct and unambiguous identification of the IPD process. Compared with dissociation without anion emission, we found typical 10-4 IPD rates, not depending much on the size and charge of the (n,q) species. Exceptions were observed for C2+ and, to a lesser extent, C43+ whose IPDs were notably lower. We tentatively interpret IPDs of C2+ and C3+ by using a statistical approach based on the counting of final states allowed by energetic criteria. The model is able to furnish the right order of magnitude for the experimental IPD rates and to provide a qualitative explanation of the lower IPD rate observed in C2+. © 2017 American Physical Society.
BibTeX:
@article{Launoy2017,
  author = {Launoy, T. and Béroff, K. and Chabot, M. and Martinet, G. and Le Padellec, A. and Pino, T. and Bouneau, S. and Vaeck, N. and Liévin, J. and Féraud, G. and Loreau, J. and Mahajan, T.},
  title = {Ion-pair dissociation of highly excited carbon clusters: Size and charge effects},
  journal = {Physical Review A},
  year = {2017},
  volume = {95},
  article number = {022711},
  doi = {10.1103/PhysRevA.95.022711}
}
Abstract: This study aims to evaluate the motion influence in the tridimensional dose distribution due to respiratory for IMRT breast planning technique. To simulate the breathing movement an oscillating platform was used. To simulate the breast, MAGIC-f phantoms were used. CT images of a static phantom were obtained and the IMRT treatment was planned based on them. One phantom was irradiated static in the platform and two other phantoms were irradiated while oscillating in the platform with amplitudes of 0.34 cm and 1.22 cm, the fourth phantom was used as reference in the MRI acquisition. The percentage of points approved in the 3D global gamma analyses (3%/3mm) when comparing the dose distribution of the static phantom with the oscillating ones was 91% for the 0.34cm amplitude and 62% for the 1.22 cm amplitude. Considering this result, the differences found in the dosimetric analyses for the oscillating amplitude of 0.34cm could be considered acceptable in a real treatment. The isodose distribution analyses showed a decrease of dose in the anterior breast region and an increase of dose on the posterior breast region, being these differences most pronounced for large amplitude motion. © Published under licence by IOP Publishing Ltd.
BibTeX:
@article{Lizar2017,
  author = {Lizar, J.C. and Santos, L.F. and Brandão, F.C. and Volpato, K.C. and Guimarães, F.S. and Pavoni, J.F.},
  title = {Evaluation of the respiratory motion influence in the 3D dose distribution of IMRT breast radiation therapy treatments},
  journal = {Journal of Physics: Conference Series},
  year = {2017},
  volume = {847},
  article number = {012031},
  doi = {10.1088/1742-6596/847/1/012031}
}
Abstract: This paper compiles our merged-beam experimental findings for the associative ionization (AI) process from charged reactants, with the aim of guiding future investigations with e.g. the double electrostatic ion storage ring DESIREE in Stockholm. A reinvestigation of the isotopic effect in H-(D-) + He+ collisions is presented, along with a review of and NO+ production by AI involving ion pairs or excited neutrals, and put in perspective with the mutual neutralization and radiative association reactions. Critical parameters are identified and evaluated for their systematic role in controlling the magnitude of the cross section: isotopic substitution, exothermicity, electronic state density, and spin statistics. © 2017 IOP Publishing Ltd.
BibTeX:
@article{Padellec2017,
  author = {Padellec, A.L. and Launoy, T. and Dochain, A. and Urbain, X.},
  title = {Investigation of critical parameters controlling the efficiency of associative ionization},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2017},
  volume = {50},
  article number = {095202},
  doi = {10.1088/1361-6455/aa6735}
}
Abstract: The excited-state quenching of [Ru(TAP)2(HAT)]2+ (TAP = 1,4,5,8-tetraazaphenanthrene, HAT= 1,4,5,8,9,12-hexaazatriphenylene) by hydroquinone (H2Q), N-acetyl-tyrosine (N-Ac-Tyr) or guanosine-5′-monophosphate (GMP) was investigated at various pH values. The quenching occurs via electron/proton transfer, as evidenced by transient absorption spectroscopy and confirmed by 1H photochemically induced dynamic nuclear polarization (photo-CIDNP). Reductive quenching also occurs in strongly acidic solution despite a much shorter lifetime of the protonated excited-state complex. Photo-CIDNP revealed a different mechanism at low pH, involving protonation before electron transfer and yielding a distinct protonated monoreduced complex. The experimental photo-CIDNP patterns are consistent with density functional theory calculations. This work highlights the power of 1H photo-CIDNP for characterizing, at the atomic level, transient species involved in electron-transfer processes. © 2017 American Chemical Society.
BibTeX:
@article{Troian-Gautier2017,
  author = {Troian-Gautier, L. and Mugeniwabagara, E. and Fusaro, L. and Cauët, E. and Kirsch-De Mesmaeker, A. and Luhmer, M.},
  title = {Photo-CIDNP Reveals Different Protonation Sites Depending on the Primary Step of the Photoinduced Electron-/Proton-Transfer Process with Ru(II) Polyazaaromatic Complexes},
  journal = {Journal of the American Chemical Society},
  year = {2017},
  volume = {139},
  pages = {14909-14912},
  doi = {10.1021/jacs.7b09513}
}
Abstract: We have used continuous-wave cavity ring-down spectroscopy to record the spectrum of H2O-Ar in the 2OH excitation range of H2O. 24 sub-bands have been observed. Their rotational structure (Trot = 12 K) is analyzed and the lines are fitted separately for ortho and para species together with microwave and far infrared data from the literature, with a unitless standard deviation σ=0.98 and 1.31, respectively. Their vibrational analysis is supported by a theoretical input based on an intramolecular potential energy surface obtained through ab initio calculations and computation of the rotational energy of sub-states of the complex with the water monomer in excited vibrational states up to the first hexad. For the ground and (010) vibrational states, the theoretical results agree well with experimental energies and rotational constants in the literature. For the excited vibrational states of the first hexad, they guided the assignment of the observed sub-bands. The upper state vibrational predissociation lifetime is estimated to be 3 ns from observed spectral linewidths. © 2017 Author(s).
BibTeX:
@article{Vanfleteren2017,
  author = {Vanfleteren, T. and Földes, T. and Herman, M. and Liévin, J. and Loreau, J. and Coudert, L.H.},
  title = {Experimental and theoretical investigations of H2O-Ar},
  journal = {Journal of Chemical Physics},
  year = {2017},
  volume = {147},
  article number = {014302},
  doi = {10.1063/1.4990738}
}
Abstract: Employing two state-of-the-art methods, multiconfiguration Dirac-Hartree-Fock and second-order many-body perturbation theory, the excitation energies and lifetimes for the lowest 200 states of the 2s22p4, 2s2p5, 2p6, 2s22p33s, 2s22p33p, 2s22p33d, 2s2p43s, 2s2p43p, and 2s2p43d configurations, and multipole (electric dipole (E1), magnetic dipole (M1), and electric quadrupole (E2)) transition rates, line strengths, and oscillator strengths among these states are calculated for each O-like ion, from Cr XVII to Zn XXIII. Our two data sets are compared with the National Institute of Standards and Technology and CHIANTI compiled values, and previous calculations. The data are accurate enough for identification and deblending of new emission lines from the Sun and other astrophysical sources. The amount of high-accuracy data is significantly increased for the n = 3 states of several O-like ions of astrophysical interest, where experimental data are very scarce. © 2017. The American Astronomical Society. All rights reserved.
BibTeX:
@article{Wang2017,
  author = {Wang, K. and Jönsson, P. and Ekman, J. and Gaigalas, G. and Godefroid, M.R. and Si, R. and Chen, Z.B. and Li, S. and Chen, C.Y. and Yan, J.},
  title = {Extended Calculations of Spectroscopic Data: Energy Levels, Lifetimes, and Transition Rates for O-like Ions from Cr xxiii},
  journal = {Astrophysical Journal, Supplement Series},
  year = {2017},
  volume = {229},
  article number = {37},
  doi = {10.3847/1538-4365/aa6847}
}
Abstract: Collinear laser spectroscopy was performed on Zn (Z=30) isotopes at ISOLDE, CERN. The study of hyperfine spectra of nuclei across the Zn isotopic chain, N=33–49, allowed the measurement of nuclear spins for the ground and isomeric states in odd-A neutron-rich nuclei up to N=50. Exactly one long-lived (>10 ms) isomeric state has been established in each 69–79Zn isotope. The nuclear magnetic dipole moments and spectroscopic quadrupole moments are well reproduced by large-scale shell–model calculations in the f5pg9 and fpg9d5 model spaces, thus establishing the dominant term in their wave function. The magnetic moment of the intruder Iπ=1/2+ isomer in 79Zn is reproduced only if the νs1/2 orbital is added to the valence space, as realized in the recently developed PFSDG-U interaction. The spin and moments of the low-lying isomeric state in 73Zn suggest a strong onset of deformation at N=43, while the progression towards 79Zn points to the stability of the Z=28 and N=50 shell gaps, supporting the magicity of 78Ni. © 2017 The Author(s)
BibTeX:
@article{Wraith2017,
  author = {Wraith, C. and Yang, X.F. and Xie, L. and Babcock, C. and Bieroń, J. and Billowes, J. and Bissell, M.L. and Blaum, K. and Cheal, B. and Filippin, L. and Garcia Ruiz, R.F. and Gins, W. and Grob, L.K. and Gaigalas, G. and Godefroid, M. and Gorges, C. and Heylen, H. and Honma, M. and Jönsson, P. and Kaufmann, S. and Kowalska, M. and Krämer, J. and Malbrunot-Ettenauer, S. and Neugart, R. and Neyens, G. and Nörtershäuser, W. and Nowacki, F. and Otsuka, T. and Papuga, J. and Sánchez, R. and Tsunoda, Y. and Yordanov, D.T.},
  title = {Evolution of nuclear structure in neutron-rich odd-Zn isotopes and isomers},
  journal = {Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics},
  year = {2017},
  volume = {771},
  pages = {385-391},
  doi = {10.1016/j.physletb.2017.05.085}
}
Abstract: Vibrationally state selective overtone spectroscopy and dynamics of weakly bound Ne-H2O complexes (D0 (para) = 31.67 cm−1, D0 (ortho) = 34.66 cm−1) are reported for the first time, based on near infrared excitation of van der Waals cluster bands correlating with vOH = 2 ← 0 overtone transitions (|02−>←|00+> and |02+>←|00+>) out of the ortho (101) and para (000) internal rotor states of the H2O moiety. Quantum theoretical calculations for nuclear motion on a high level ab initio potential energy surface (CCSD(T)/VnZ-f12 (n = 3,4), corrected for basis set superposition error and extrapolated to the complete basis set limit) are employed for assignment of Σ←Σ,Π←Σ, and Σ←Π infrared bands in the overtone spectra, where Σ(K = 0) and Π (K = 1) represent approximate projections (K) of the body angular momentum along the Ne-H2O internuclear axis. End-over-end tumbling of the ortho Ne-H2O cluster is evident via rotational band contours observed, with band origins and rotational progressions in excellent agreement with ab initio frequency and intensity predictions. A clear Q branch in the corresponding |02+>fΠ(111)←eΣ(000) para Ne-H2O spectrum provides evidence for a novel e/f parity-dependent metastability in these weakly bound clusters, in agreement with ab initio bound state calculations and attributable to the symmetry blocking of an energetically allowed channel for internal rotor predissociation. Finally, Boltzmann analysis of the rotational spectra reveals anomalously low jet temperatures (Trot ≈ 4(1) K), which are attributed to “evaporative cooling” of weakly bound Ne-H2O clusters and provide support for similar cooling dynamics in rare gas-tagging studies. © 2017 Author(s).
BibTeX:
@article{Ziemkiewicz2017,
  author = {Ziemkiewicz, M.P. and Pluetzer, C. and Wojcik, M. and Loreau, J. and Van der Avoird, A. and Nesbitt, D.J.},
  title = {Near infrared overtone (vOH = 2 ← 0) spectroscopy of Ne-H2O clusters},
  journal = {Journal of Chemical Physics},
  year = {2017},
  volume = {146},
  article number = {104204},
  doi = {10.1063/1.4977061}
}
Abstract: Collinear laser spectroscopy on Cu58-75 isotopes was performed at the CERN-ISOLDE radioactive ion beam facility. In this paper we report on the isotope shifts obtained from these measurements. State-of-the-art atomic physics calculations have been undertaken in order to determine the changes in mean-square charge radii δ(r2)A,A′ from the observed isotope shifts. A local minimum is observed in these radii differences at N=40, providing evidence for a weak N=40 sub-shell effect. However, comparison of δ(r2)A,A′ with a droplet model prediction including static deformation deduced from the spectroscopic quadrupole moments, points to the persistence of correlations at N=40. © 2016 authors. Published by the American Physical Society.
BibTeX:
@article{Bissell2016,
  author = {Bissell, M.L. and Carette, T. and Flanagan, K.T. and Vingerhoets, P. and Billowes, J. and Blaum, K. and Cheal, B. and Fritzsche, S. and Godefroid, M. and Kowalska, M. and Krämer, J. and Neugart, R. and Neyens, G. and Nörtershäuser, W. and Yordanov, D.T.},
  title = {Cu charge radii reveal a weak sub-shell effect at N=40},
  journal = {Physical Review C},
  year = {2016},
  volume = {93},
  article number = {064318},
  doi = {10.1103/PhysRevC.93.064318}
}
Abstract: We present here a 2D model of photochemistry for computing the production and loss mechanisms of the O(1S) and O(1D) states, which are responsible for the emission lines at 577.7, 630, and 636.4 nm, in case of the comet 1P/Halley. The presence of O2 within cometary atmospheres, measured by the in situ Rosetta and Giotto missions, necessitates a revision of the usual photochemical models. Indeed, the photodissociation of molecular oxygen also leads to a significant production of oxygen in excited electronic states. In order to correctly model the solar ultraviolet (UV) flux absorption, we consider here a 2D configuration. While the green to red-doublet ratio is not affected by the solar UV flux absorption, estimates of the red-doublet and green lines emissions are, however, overestimated by a factor of 2 in the 1D model compared to the 2D model. Considering a spherical symmetry, emission maps can be deduced from the 2D model in order to be directly compared to ground and/or in situ observations. © 2017 The Authors.
BibTeX:
@article{Cessateur2016,
  author = {Cessateur, G. and De Keyser, J. and Maggiolo, R. and Rubin, M. and Gronoff, G. and Gibbons, A. and Jehin, E. and Dhooghe, F. and Gunell, H. and Vaeck, N. and Loreau, J.},
  title = {2D photochemical model for forbidden oxygen line emission for comet 1P/Halley},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {2016},
  volume = {462},
  pages = {S116-S123},
  doi = {10.1093/mnras/stw2150}
}
Abstract: Observations of the green and red-doublet emission lines have previously been realized for several comets. We present here a chemistry-emission coupled model to study the production and loss mechanisms of the O(1S) and O(1D) states, which are responsible for the emission lines of interest for comet 67P/Churyumov-Gerasimenko. The recent discovery of O2 in significant abundance relative to water 3.80 ± 0.85 within the coma of 67P has been taken into consideration for the first time in such models. We evaluate the effect of the presence of O2 on the green to red-doublet emission intensity ratio, which is traditionally used to assess the CO2 abundance within cometary atmospheres. Model simulations, solving the continuity equation with transport, show that not taking O2 into account leads to an underestimation of the CO2 abundance within 67P, with a relative error of about 25%. This strongly suggests that the green to red-doublet emission intensity ratio alone is not a proper tool for determining the CO2 abundance, as previously suggested. Indeed, there is no compelling reason why O2 would not be a common cometary volatile, making revision of earlier assessments regarding the CO2 abundance in cometary atmospheres necessary. The large uncertainties of the CO2 photodissociation cross section imply that more studies are required in order to better constrain the O(1S) and O(1D) production through this mechanism. Space weather phenomena, such as powerful solar flares, could be used as tools for doing so, providing additional information on a good estimation of the O2 abundance within cometary atmospheres. ©2016. The Authors.
BibTeX:
@article{Cessateur2016a,
  author = {Cessateur, G. and Keyser, J.D. and Maggiolo, R. and Gibbons, A. and Gronoff, G. and Gunell, H. and Dhooghe, F. and Loreau, J. and Vaeck, N. and Altwegg, K. and Bieler, A. and Briois, C. and Calmonte, U. and Combi, M.R. and Fiethe, B. and Fuselier, S.A. and Gombosi, T.I. and Hässig, M. and Le Roy, L. and Neefs, E. and Rubin, M. and Sémon, T.},
  title = {Photochemistry of forbidden oxygen lines in the inner coma of 67P/Churyumov-Gerasimenko},
  journal = {Journal of Geophysical Research A: Space Physics},
  year = {2016},
  volume = {121},
  pages = {804-816},
  doi = {10.1002/2015JA022013}
}
Abstract: Threshold-photoionization spectroscopy of cyanoacetylene (HC3N) and its 15N isotopologue has been investigated in the vacuum-ultraviolet range with a synchrotron-based experiment allowing to record threshold-photoelectron spectrum and photoion yield over a large energy range (from 88 500 to 177 500 cm-1, i.e., from 11 to 22 eV). Adiabatic ionization energies towards the three lowest electronic states X+ 2Π, A+ Σ+2, and B+ Π2 are derived from the threshold-photoelectron spectrum. A detailed description of the vibrational structure of these states is proposed leading to the determination of the vibrational frequencies for most modes. The vibrational assignments and the discussion about the electronic structure are supported by multireference ab initio calculations (CASPT2, MRCI). Unprecedented structures are resolved and tentatively assigned in the region of the B+ X transition. Exploratory calculations highlight the complexity of the electronic landscape of the cation up to approximately 10 eV above its ground state. © 2016 Author(s).
BibTeX:
@article{Desrier2016,
  author = {Desrier, A. and Romanzin, C. and Lamarre, N. and Alcaraz, C. and Gans, B. and Gauyacq, D. and Liévin, J. and Boyé-Péronne, S.},
  title = {Experimental and ab initio characterization of HC3N+ vibronic structure. I. Synchrotron-based threshold photo-electron spectroscopy},
  journal = {Journal of Chemical Physics},
  year = {2016},
  volume = {145},
  article number = {234310},
  doi = {10.1063/1.4972019}
}
Abstract: The present work reports results from systematic multiconfiguration Dirac-Hartree-Fock calculations of electronic isotope shift factors for a set of transitions between low-lying levels of neutral aluminium. These electronic quantities together with observed isotope shifts between different pairs of isotopes provide the changes in mean-square charge radii of the atomic nuclei. Two computational approaches are adopted for the estimation of the mass- and field-shift factors. Within these approaches, different models for electron correlation are explored in a systematic way to determine a reliable computational strategy and to estimate theoretical error bars of the isotope shift factors. © 2016 American Physical Society.
BibTeX:
@article{Filippin2016a,
  author = {Filippin, L. and Beerwerth, R. and Ekman, J. and Fritzsche, S. and Godefroid, M. and Jönsson, P.},
  title = {Multiconfiguration calculations of electronic isotope shift factors in Al i},
  journal = {Physical Review A},
  year = {2016},
  volume = {94},
  article number = {062508},
  doi = {10.1103/PhysRevA.94.062508}
}
Abstract: Relativistic two-photon decay rates of the 2s1/2 and 2p1/2 states towards the 1s1/2 ground state of hydrogenic atoms are calculated by using numerically exact energies and wave functions obtained from the Dirac equation with the Lagrange-mesh method. This approach is an approximate variational method taking the form of equations on a grid because of the use of a Gauss quadrature approximation. Highly accurate values are obtained by a simple calculation involving different meshes for the initial, final, and intermediate wave functions and for the calculation of matrix elements. The accuracy of the results with a Coulomb potential is improved by several orders of magnitude in comparison with benchmark values from the literature. The general requirement of gauge invariance is also successfully tested, down to rounding errors. The method provides high accuracies for two-photon decay rates of a particle in other potentials and is applied to a hydrogen atom embedded in a Debye plasma simulated by a Yukawa potential. © 2016 American Physical Society.
BibTeX:
@article{Filippin2016,
  author = {Filippin, L. and Godefroid, M. and Baye, D.},
  title = {Relativistic two-photon decay rates with the Lagrange-mesh method},
  journal = {Physical Review A},
  year = {2016},
  volume = {93},
  article number = {012517},
  doi = {10.1103/PhysRevA.93.012517}
}
Abstract: The present work reports results from systematic multiconfiguration Dirac-Hartree-Fock calculations of isotope shifts for several well-known transitions in neutral magnesium. Relativistic normal and specific mass shift factors as well as the electronic probability density at the origin are calculated. Combining these electronic quantities with available nuclear data, energy and transition level shifts are determined for the Mg26-Mg24 pair of isotopes. Different models for electron correlation are adopted. It is shown that, although valence and core-valence models provide accurate values for the isotope shifts, the inclusion of core-core excitations in the computational strategy significantly improves the accuracy of the transition energies and normal mass shift factors. © 2016 American Physical Society.
BibTeX:
@article{Filippin2016b,
  author = {Filippin, L. and Godefroid, M. and Ekman, J. and Jönsson, P.},
  title = {Core correlation effects in multiconfiguration calculations of isotope shifts in Mg I},
  journal = {Physical Review A},
  year = {2016},
  volume = {93},
  article number = {062512},
  doi = {10.1103/PhysRevA.93.062512}
}
Abstract: Multiconfiguration wave function expansions combined with configuration interaction methods are a method of choice for complex atoms where atomic state functions are expanded in a basis of configuration state functions. Combined with a variational method such as the multiconfiguration Hartree-Fock (MCHF) or multiconfiguration Dirac-Hartree-Fock (MCDHF), the associated set of radial functions can be optimized for the levels of interest. The present review updates the variational MCHF theory to include MCDHF, describes the multireference single and double process for generating expansions and the systematic procedure of a computational scheme for monitoring convergence. It focuses on the calculations of energies and wave functions from which other atomic properties can be predicted such as transition rates, hyperfine structures and isotope shifts, for example. © 2016 IOP Publishing Ltd.
BibTeX:
@article{Fischer2016,
  author = {Fischer, C.F. and Godefroid, M. and Brage, T. and Jönsson, P. and Gaigalas, G.},
  title = {Advanced multiconfiguration methods for complex atoms: I. Energies and wave functions},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2016},
  volume = {49},
  article number = {182004},
  doi = {10.1088/0953-4075/49/18/182004}
}
Abstract: Vacuum-ultraviolet pulsed-field-ionization zero-kinetic-energy photoelectron spectra of X+Π2←XΣ+1 and B+Π2←XΣ+1 transitions of the HC314N and HC315N isotopologues of cyanoacetylene have been recorded. The resolution of the photoelectron spectra allowed us to resolve the vibrational structures and the spin-orbit splittings in the cation. Accurate values of the adiabatic ionization potentials of the two isotopologues (EI/hc(HC314N)=93 909(2) cm-1 and EI/hc(HC315N)=93 912(2) cm-1), the vibrational frequencies of the ν2, ν6, and ν7 vibrational modes, and the spin-orbit coupling constant (ASO = -44(2) cm-1) of the X+Π2 cationic ground state have been derived from the measurements. Using ab initio calculations, the unexpected structure of the B+Π2←XΣ+1 transition is tentatively attributed to a conical intersection between the A+ and B+ electronic states of the cation. © 2016 Author(s).
BibTeX:
@article{Gans2016,
  author = {Gans, B. and Lamarre, N. and Broquier, M. and Liévin, J. and Boyé-Péronne, S.},
  title = {Experimental and ab initio characterization of HC3N+ vibronic structure. II. High-resolution VUV PFI-ZEKE spectroscopy},
  journal = {Journal of Chemical Physics},
  year = {2016},
  volume = {145},
  article number = {234309},
  doi = {10.1063/1.4972018}
}
Abstract: Mathematical models have provided important insights into acute viral dynamics within individual patients. In this paper, we study the simplest target cell-limited models to investigate the within-host dynamics of influenza A virus infection in humans. Despite the biological simplicity of the models, we show how these can be used to understand the severity of the infection and the key attributes of possible immunotherapy and antiviral drugs for the treatment of infection at different times post infection. Through an analytic approach, we derive and estimate simple summary biological quantities that can provide novel insights into the infection dynamics and the definition of clinical endpoints. We focus on nine quantities, including the area under the viral load curve, peak viral load, the time to peak viral load and the level of cell death due to infection. Using Markov chain Monte Carlo methods, we fitted the models to data collected from 12 untreated volunteers who participated in two clinical studies that tested the antiviral drugs oseltamivir and zanamivir. Based on the results, we also discuss various difficulties in deriving precise estimates of the parameters, even in the very simple models considered, when experimental data are limited to viral load measures and/or there is a limited number of viral load measurements post infection. © 2016 The Authors.
BibTeX:
@article{Hadjichrysanthou2016,
  author = {Hadjichrysanthou, C. and Cauët, E. and Lawrence, E. and Vegvari, C. and De Wolf, F. and Anderson, R.M.},
  title = {Understanding the within-host dynamics of influenza A virus: From theory to clinical implications},
  journal = {Journal of the Royal Society Interface},
  year = {2016},
  volume = {13},
  article number = {20160289},
  doi = {10.1098/rsif.2016.0289}
}
Abstract: Multiconfiguration Dirac-Hartree-Fock (MCDHF) calculations and relativistic configuration interaction (RCI) calculations are performed for states of the 3s23p2, 3s3p3 and 3s23p3d configurations in the Si-like ions Ti IX - Ge XIX, Sr XXV, Zr XXVII and Mo XXIX. Valence and core-valence electron correlation effects are accounted for through large configuration state function expansions. Calculated energy levels are compared with data from other calculations and with experimental data from the reference databases. Lifetime and transition rates along with uncertainty estimations are given for all ions. Energies from the calculations are in excellent agreement with observations and computed wavelength are almost of spectroscopic accuracy, aiding line identification in spectra. © 2015 ESO.
BibTeX:
@article{Joensson2016,
  author = {Jönsson, P. and Radžiute, L. and Gaigalas, G. and Godefroid, M.R. and Marques, J.P. and Brage, T. and Froese Fischer, C. and Grant, I.P.},
  title = {Accurate multiconfiguration calculations of energy levels, lifetimes, and transition rates for the silicon isoelectronic sequence: Ti IX - Ge XIX, Sr XXV, Zr XXVII, Mo XXIX},
  journal = {Astronomy and Astrophysics},
  year = {2016},
  volume = {585},
  article number = {A26},
  doi = {10.1051/0004-6361/201527106}
}
Abstract: A theoretical rate constant for the associative detachment reaction Rb(2S) + OH-(1Σ+) → RbOH(1Σ+) + e- of 4 × 10-10 cm3 s-1 at 300 K has been calculated. This result agrees with the experimental rate constant of 2 - 1 + 2 × 1 0 - 10 cm 3 s - 1 obtained by Deiglmayr et al. [Phys. Rev. A 86, 043438 (2012)] for a temperature between 200 K and 600 K. A Langevin-based dynamics which depends on the crossing point between the anion (RbOH-) and neutral (RbOH) potential energy surfaces has been used. The calculations were performed using the ECP28MDF effective core potential to describe the rubidium atom at the CCSD(T) level of theory and extended basis sets. The effect of ECPs and basis set on the height of the crossing point, and hence the rate constant, has been investigated. The temperature dependence of the latter is also discussed. Preliminary work on the potential energy surface for the excited reaction channel Rb(2P) + OH-(1Σ+) calculated at the CASSCF-icMRCI level of theory is presented. We qualitatively discuss the charge transfer and associative detachment reactions arising from this excited entrance channel. © 2016 Author(s).
BibTeX:
@article{Kas2016,
  author = {Kas, M. and Loreau, J. and Liévin, J. and Vaeck, N.},
  title = {Ab initio study of reactive collisions between Rb(2 S) or Rb(2 P) and OH-(1Σ+)},
  journal = {Journal of Chemical Physics},
  year = {2016},
  volume = {144},
  article number = {204306},
  doi = {10.1063/1.4950784}
}
Abstract: We calculated the magnetic dipole hyperfine interaction constants and the electric field gradients of and levels of Ne I by using the multiconfiguration Dirac-Hartree-Fock method. The electronic factors contributing to the isotope shifts were also estimated for the transition connecting these two states. Electron correlation and relativistic effects including the Breit interaction were investigated in detail. Combining with recent measurements, we extracted the nuclear quadrupole moment values for 20Ne and 23Ne with a smaller uncertainty than the current available data. Isotope shifts in the transition based on the present calculated field- and mass-shift parameters are in good agreement with the experimental values. However, the field shifts in this transition are two or three orders of magnitude smaller than the mass shifts, making rather difficult to deduce changes in nuclear-charge mean-square radii. According to our theoretical predictions, we suggest using instead transitions connecting levels arising from the 2p53s configuration to the ground state, for which the normal mass shift and specific mass shift contributions counteract each other, producing relatively small mass shifts that are only one order of magnitude larger than relatively large field shifts, especially for the transition. © 2016 IOP Publishing Ltd.
BibTeX:
@article{Li2016,
  author = {Li, J. and Godefroid, M. and Wang, J.},
  title = {Atomic parameters for the 2{p}^{5}3p\;{}^{2}{[3/2]}-{2}-2{p}^{5}3s\;{}^{2}{[3/2]}-{2}^{o}transition of Ne i relevant in nuclear physics},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2016},
  volume = {49},
  article number = {115002},
  doi = {10.1088/0953-4075/49/11/115002}
}
Abstract: Background About 90% of drugs fail in clinical development. The question is whether trials fail because of insufficient efficacy of the new treatment, or rather because of poor trial design that is unable to detect the true efficacy. The variance of the measured endpoints is a major, largely underestimated source of uncertainty in clinical trial design, particularly in acute viral infections. We use a clinical trial simulator to demonstrate how a thorough consideration of the variability inherent in clinical trials of novel therapies for acute viral infections can improve trial design. Methods and Findings We developed a clinical trial simulator to analyse the impact of three different types of variation on the outcome of a challenge study of influenza treatments for infected patients, including individual patient variability in the response to the drug, the variance of the measurement procedure, and the variance of the lower limit of quantification of endpoint measurements. In addition, we investigated the impact of protocol variation on clinical trial outcome. We found that the greatest source of variance was inter-individual variability in the natural course of infection. Running a larger phase II study can save up to $38 million, if an unlikely to succeed phase III trial is avoided. In addition, low-sensitivity viral load assays can lead to falsely negative trial outcomes. Conclusions Due to high inter-individual variability in natural infection, the most important variable in clinical trial design for challenge studies of potential novel influenza treatments is the number of participants. 100 participants are preferable over 50. Using more sensitive viral load assays increases the probability of a positive trial outcome, but may in some circumstances lead to false positive outcomes. Clinical trial simulations are powerful tools to identify the most important sources of variance in clinical trials and thereby help improve trial design. © 2016 Vegvari et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
BibTeX:
@article{Vegvari2016,
  author = {Vegvari, C. and Cauët, E. and Hadjichrysanthou, C. and Lawrence, E. and Weverling, G.-J. and De Wolf, F. and Anderson, R.M.},
  title = {Using clinical trial simulators to analyse the sources of variance in clinical trials of novel therapies for acute viral infections},
  journal = {PLoS ONE},
  year = {2016},
  volume = {11},
  article number = {e0156622},
  doi = {10.1371/journal.pone.0156622}
}
Abstract: Acute viral infections pose many practical challenges for the accurate assessment of the impact of novel therapies on viral growth and decay. Using the example of influenza A, we illustrate how the measurement of infection-related quantities that determine the dynamics of viral load within the human host, can inform investigators on the course and severity of infection and the efficacy of a novel treatment. We estimated the values of key infection-related quantities that determine the course of natural infection from viral load data, using Markov Chain Monte Carlo methods. The data were placebo group viral load measurements collected during volunteer challenge studies, conducted by Roche, as part of the oseltamivir trials. We calculated the values of the quantities for each patient and the correlations between the quantities, symptom severity and body temperature. The greatest variation among individuals occurred in the viral load peak and area under the viral load curve. Total symptom severity correlated positively with the basic reproductive number. The most sensitive endpoint for therapeutic trials with the goal to cure patients is the duration of infection. We suggest laboratory experiments to obtain more precise estimates of virological quantities that can supplement clinical endpoint measurements. © 2016 Vegvari et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
BibTeX:
@article{Vegvari2016a,
  author = {Vegvari, C. and Hadjichrysanthou, C. and Cauët, E. and Lawrence, E. and Cori, A. and De Wolf, F. and Anderson, R.M.},
  title = {How can viral dynamics models inform endpoint measures in clinical trials of therapies for acute viral infections?},
  journal = {PLoS ONE},
  year = {2016},
  volume = {11},
  article number = {e0158237},
  doi = {10.1371/journal.pone.0158237}
}
Abstract: The semiclassical formalism of Robert and Bonamy is used to calculate the linewidths of rovibrational transitions of ammonia in collision with argon. Two accurate ab initio potential energy surfaces (PES) have been applied to model the NH3-Ar interactions. In this work and contrary to our previous calculations, the transitions with ΔK = ±3n (n integer) have been introduced into the expressions of the differential collision cross section S(b). Comparisons with previous theoretical and experimental studies are reported. A detailed analysis of the contribution of the various anisotropic components of the PES shows that the induced ΔK = ±3 transitions play a crucial role. Calculations performed in the ν4 and ν1 vibrational bands of NH3 are in good agreement with the experimental data and correct dependences of the broadening coefficients with the rotational quantum numbers J and K are obtained. © 2015 Published by Elsevier Inc.
BibTeX:
@article{Ayari2015,
  author = {Ayari, C. and Loreau, J. and Dhib, M. and Daussy, C. and Aroui, H.},
  title = {Semiclassical line broadening calculations using an ab initio potential. Application to NH3 perturbed by argon},
  journal = {Journal of Molecular Spectroscopy},
  year = {2015},
  volume = {318},
  pages = {46-52},
  doi = {10.1016/j.jms.2015.09.011}
}
BibTeX:
@article{Berger2015,
  author = {Berger, G. and Gelbcke, M. and Cauët, E. and Luhmer, M. and Nève, J. and Dufrasne, F.},
  title = {Erratum:Corrigendum to "synthesis of 15N-labeled vicinal diamines through N-activated chiral aziridines: Tools for the NMR study of platinum-based anticancer compounds" (Tetrahedron Letters (2013) 54 (545-548) doi:10.1016/j.tetlet.2014.11.086))},
  journal = {Tetrahedron Letters},
  year = {2015},
  volume = {56},
  pages = {485},
  doi = {10.1016/j.tetlet.2014.11.086}
}
Abstract: The Double Focusing Mass Spectrometer (DFMS), part of the ROSINA instrument package aboard the European Space Agency's Rosetta spacecraft visiting comet 67P/Churyumov-Gerasimenko, experiences minor deformation of the mass peaks in the high resolution spectra acquired for m/Z = 16, 17, and to a lesser extent 18. A numerical deconvolution technique has been developed with a twofold purpose. A first goal is to verify whether the most likely cause of the issue, a lack of stability of one of the electric potentials in the electrostatic analyser, can indeed be held responsible for it. The second goal is to correct for the deformation, in view of the important species located around these masses, and to allow a standard further treatment of the spectra in the automated DFMS data processing chain. © 2015 The Authors. Published by Elsevier B.V.
BibTeX:
@article{DeKeyser2015,
  author = {De Keyser, J. and Dhooghe, F. and Gibbons, A. and Altwegg, K. and Balsiger, H. and Berthelier, J.-J. and Briois, C. and Calmonte, U. and Cessateur, G. and Equeter, E. and Fiethe, B. and Fuselier, S.A. and Gombosi, T.I. and Gunell, H. and Hässig, M. and Le Roy, L. and Maggiolo, R. and Neefs, E. and Rubin, M. and Sémon, T.},
  title = {Correcting peak deformation in Rosetta's ROSINA/DFMS mass spectrometer},
  journal = {International Journal of Mass Spectrometry},
  year = {2015},
  volume = {393},
  pages = {41-51},
  doi = {10.1016/j.ijms.2015.10.010}
}
Abstract: We have investigated the N2O-HDO molecular complex using ab initio calculations at the CCSD(T)-F12a/aug-cc-pVTZ level of theory and using cavity ring-down spectroscopy to probe an HDO/N2O/Ar supersonic jet around 1.58 m. A single a-type vibrational band was observed, 13 cm-1 redshifted compared to the OH+OD excited band in HDO, and 173 vibration-rotation lines were assigned (Trot ≈ 20 K). A weighted fit of existing microwave and present near infrared (NIR) data was achieved using a standard Watson's Hamiltonian (σ = 1.26), producing ground and excited states rotational constants. The comparison of the former with those calculated ab initio suggests a planar geometry in which the OD rather than the OH bond in water is almost parallel to NNO. The equilibrium geometry and dissociation energy (De = -11.7 kJ/mol) of the water-nitrous oxide complex were calculated. The calculations further demonstrate and allow characterising another minimum, 404 cm-1 (ΔE0) higher in energy. Harmonic vibrational frequencies and dissociation energies, D0, were calculated for various conformers and isotopic forms of the complex, in both minima. The absence of N2O-D2O from dedicated NIR experiments is reported and discussed. © 2014 Taylor & Francis.
BibTeX:
@article{Foeldes2015,
  author = {Földes, T. and Lauzin, C. and Vanfleteren, T. and Herman, M. and Liévin, J. and Didriche, K.},
  title = {High-resolution, near-infrared CW-CRDS, and ab initio investigations of N2O-HDO},
  journal = {Molecular Physics},
  year = {2015},
  volume = {113},
  pages = {473-482},
  doi = {10.1080/00268976.2014.953611}
}
Abstract: Recently there has been a renewed interest in the chemical physics literature of factorization of the position representation eigenfunctions φ of the molecular Schrödinger equation as originally proposed by Hunter in the 1970s. The idea is to represent φ in the form φχ where χ is purely a function of the nuclear coordinates, while φ must depend on both electron and nuclear position variables in the problem. This is a generalization of the approximate factorization originally proposed by Born and Oppenheimer, the hope being that an 'exact' representation of φ can be achieved in this form with φ and χ interpretable as 'electronic' and 'nuclear' wavefunctions respectively. We offer a mathematical analysis of these proposals that identifies ambiguities stemming mainly from the singularities in the Coulomb potential energy. © 2015 IOP Publishing Ltd.
BibTeX:
@article{Jecko2015,
  author = {Jecko, T. and Sutcliffe, B.T. and Woolley, R.G.},
  title = {On factorization of molecular wavefunctions},
  journal = {Journal of Physics A: Mathematical and Theoretical},
  year = {2015},
  volume = {48},
  article number = {445201},
  doi = {10.1088/1751-8113/48/44/445201}
}
Abstract: Ion-pair dissociation of a highly excited molecule is a relaxation process giving rise to emission of anionic and cationic fragments. We present first measurements of ion-pair dissociation of carbon clusters. We found that ion- pair relaxation is an ubiquitous, although very small, relaxation channel common to all sizes and charges of Cq+n species produced in high velocity C+n-He collisions. Quantitative interpretation of measured branching ratios is conducted on the basis of a statistical approach i.e through listing of all possible final states. © Published under licence by IOP Publishing Ltd.
BibTeX:
@article{Launoy2015,
  author = {Launoy, T. and Chabot, M. and Martinet, G. and Pino, T. and Le Padellec, A. and Bouneau, S. and Féraud, G. and Do Thi, N. and Vaeck, N. and Liévin, J. and Loreau, J. and Béroff, K.},
  title = {Ion-pair dissociation of highly excited carbon clusters, size and charge effects},
  journal = {Journal of Physics: Conference Series},
  year = {2015},
  volume = {635},
  article number = {032085},
  doi = {10.1088/1742-6596/635/3/032085}
}
Abstract: Ion pair collisions are an important process in many astrophysical environments. We present ab initio calculations of highly excited states of C2+ and identify the ion pair channel C2+/C-. We use these results to interpret recent experiments on carbon cluster dissociation. © Published under licence by IOP Publishing Ltd.
BibTeX:
@article{Launoy2015a,
  author = {Launoy, T. and Vaeck, N. and Urbain, X. and Liévin, J. and Loreau, J. and Béroff, K. and Chabot, M.},
  title = {On the reactivity of ion pairs into different diatomic systems},
  journal = {Journal of Physics: Conference Series},
  year = {2015},
  volume = {635},
  article number = {022018},
  doi = {10.1088/1742-6596/635/2/022018}
}
Abstract: We present a theoretical study of elastic and rotationally inelastic collisions of NH3 and ND3 with rare gas atoms (He, Ne, Ar, Kr, Xe) at low energy. Quantum close-coupling calculations have been performed for energies between 0.001 and 300 cm-1. We focus on collisions in which NH3 is initially in the upper state of the inversion doublet with j = 1, k = 1, which is the most relevant in an experimental context as it can be trapped electrostatically and Stark-decelerated. We discuss the presence of resonances in the elastic and inelastic cross sections, as well as the trends in the inelastic cross sections along the rare gas series and the differences between NH3 and ND3 as a colliding partner. We also demonstrate the importance of explicitly taking into account the umbrella (inversion) motion of NH3 in order to obtain accurate scattering cross sections at low collision energy. Finally, we investigate the possibility of sympathetic cooling of ammonia using cold or ultracold rare gas atoms. We show that some systems exhibit a large ratio of elastic to inelastic cross sections in the cold regime, which is promising for sympathetic cooling experiments. The close-coupling calculations are based on previously reported ab initio potential energy surfaces for NH3-He and NH3-Ar, as well as on new, four-dimensional, potential energy surfaces for the interaction of ammonia with Ne, Kr, and Xe, which were computed using the coupled-cluster method and large basis sets. We compare the properties of the potential energy surfaces corresponding to the interaction of ammonia with the various rare gas atoms. © 2015 AIP Publishing LLC.
BibTeX:
@article{Loreau2015,
  author = {Loreau, J. and Van Der Avoird, A.},
  title = {Scattering of NH3 and ND3 with rare gas atoms at low collision energy},
  journal = {Journal of Chemical Physics},
  year = {2015},
  volume = {143},
  article number = {184303},
  doi = {10.1063/1.4935259}
}
Abstract: We present theoretical studies on the scattering resonances in rotationally inelastic collisions of NH3 and ND3 molecules with H2 molecules. We use the quantum close-coupling method to compute state-to-state integral and differential cross sections for the NH3/ND3-H2 system for collision energies between 5 and 70 cm-1, using a previously reported potential energy surface [Maret et al., Mon. Not. R. Astron. Soc. 399, 425 (2009)]. We identify the resonances as shape or Feshbach resonances. To analyze these, we use an adiabatic bender model, as well as examination at the scattering wave functions and lifetimes. The strength and width of the resonance peaks suggest that they could be observed in a crossed molecular beam experiment involving a Stark-decelerated NH3 beam. © 2015 AIP Publishing LLC.
BibTeX:
@article{Ma2015,
  author = {Ma, Q. and Van Der Avoird, A. and Loreau, J. and Alexander, M.H. and Van De Meerakker, S.Y.T. and Dagdigian, P.J.},
  title = {Resonances in rotationally inelastic scattering of NH3 and ND3 with H2},
  journal = {Journal of Chemical Physics},
  year = {2015},
  volume = {143},
  article number = {044312},
  doi = {10.1063/1.4927074}
}
Abstract: The present work deals with a set of problems in isotope shifts of neutral barium spectral lines. Some well-known transitions (6s21S0-6s6p1,3P1o and 6s21S0-6p23P0) are investigated. Values of the changes in the nuclear mean-square charge radius are deduced from the available experimental isotope shifts using our ab initio electronic factors. The three sets δ r2A,A′ obtained from these lines are consistent with each other. The combination of the available nuclear mean-square radii with our electronic factors for the 6s5d3D1,2-6s6p1P1o transitions produces isotope shift values in conflict with the laser spectroscopy measurements of U. Dammalapati et al. [Eur. Phys. J. D 53, 1 (2009)EPJDF61434-606010.1140/epjd/e2009-00076-x]. © 2015 American Physical Society.
BibTeX:
@article{Naze2015,
  author = {Nazé, C. and Li, J.G. and Godefroid, M.},
  title = {Theoretical isotope shifts in neutral barium},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2015},
  volume = {91},
  article number = {032511},
  doi = {10.1103/PhysRevA.91.032511}
}
Abstract: Optimal control theory has been employed to populate separately two dark states of the acetylene polyad, Ns = 1 and Nr = 5, by indirect coupling via the ground state. Relevant level energies and transition dipole moments are extracted from the experimental literature. The optimal pulses are rather simple. The evolution of the population is shown for the duration of the control process and also for the field-free evolution that follows the control. One of the dark states appears to be a potential target for realistic experimental investigation because the average population of the Rabi oscillation remains high and decoherence is expected to be weak. © 2015 Taylor and Francis.
BibTeX:
@article{Santos2015a,
  author = {Santos, L. and Iacobellis, N. and Herman, M. and Perry, D.S. and Desouter-Lecomte, M. and Vaeck, N.},
  title = {A test of optimal laser impulsion for controlling population within the N s = 1, N r = 5 polyad of 12C 2H 2},
  journal = {Molecular Physics},
  year = {2015},
  volume = {113},
  pages = {4000-4006},
  doi = {10.1080/00268976.2015.1102980}
}
Abstract: Following a recent proposal of L. Wang and D. Babikov [J. Chem. Phys. 137, 064301 (2012)], we theoretically illustrate the possibility of using the motional states of a Cd+ ion trapped in a slightly anharmonic potential to simulate the single-particle time-dependent Schrödinger equation. The simulated wave packet is discretized on a spatial grid and the grid points are mapped on the ion motional states which define the qubit network. The localization probability at each grid point is obtained from the population in the corresponding motional state. The quantum gate is the elementary evolution operator corresponding to the time-dependent Schrödinger equation of the simulated system. The corresponding matrix can be estimated by any numerical algorithm. The radio-frequency field which is able to drive this unitary transformation among the qubit states of the ion is obtained by multi-target optimal control theory. The ion is assumed to be cooled in the ground motional state, and the preliminary step consists in initializing the qubits with the amplitudes of the initial simulated wave packet. The time evolution of the localization probability at the grids points is then obtained by successive applications of the gate and reading out the motional state population. The gate field is always identical for a given simulated potential, only the field preparing the initial wave packet has to be optimized for different simulations. We check the stability of the simulation against decoherence due to fluctuating electric fields in the trap electrodes by applying dissipative Lindblad dynamics. © 2015 AIP Publishing LLC.
BibTeX:
@article{Santos2015,
  author = {Santos, L. and Justum, Y. and Vaeck, N. and Desouter-Lecomte, M.},
  title = {Simulation of the elementary evolution operator with the motional states of an ion in an anharmonic trap},
  journal = {Journal of Chemical Physics},
  year = {2015},
  volume = {142},
  article number = {134304},
  doi = {10.1063/1.4916355}
}
Abstract: A new approach to simulating rotational cooling using a direct simulation Monte Carlo (DSMC) method is described and applied to the rotational cooling of ammonia seeded into a helium supersonic jet. The method makes use of ab initio rotational state changing cross sections calculated as a function of collision energy. Each particle in the DSMC simulations is labelled with a vector of rotational populations that evolves with time. Transfer of energy into translation is calculated from the mean energy transfer for this population at the specified collision energy. The simulations are compared with a continuum model for the on-axis density, temperature and velocity; rotational temperature as a function of distance from the nozzle is in accord with expectations from experimental measurements. The method could be applied to other types of gas mixture dynamics under non-uniform conditions, such as buffer gas cooling of NH3 by He. © 2015 Taylor and Francis.
BibTeX:
@article{Schullian2015,
  author = {Schullian, O. and Loreau, J. and Vaeck, N. and Avoird, A.V.D. and Heazlewood, B.R. and Rennick, C.J. and Softley, T.P.},
  title = {Simulating rotationally inelastic collisions using a direct simulation Monte Carlo method},
  journal = {Molecular Physics},
  year = {2015},
  volume = {113},
  pages = {3972-3978},
  doi = {10.1080/00268976.2015.1098740}
}
BibTeX:
@article{Softley2015,
  author = {Softley, T. and Herman, M. and Vaeck, N.},
  title = {Special issue on atomic and molecular collision mechanisms},
  journal = {Molecular Physics},
  year = {2015},
  volume = {113},
  pages = {3917},
  doi = {10.1080/00268976.2015.1114702}
}
Abstract: An examination is made of the way in which the kinetic energy operator for internal motion alone is commonly constructed in molecular quantum mechanics. It is shown that some care needs to be taken to specify the precise conditions under which the form of the operator so obtained is a valid form. Particular care is needed in constructing a reaction path Hamiltonian. © 2015 Taylor & Francis.
BibTeX:
@article{Sutcliffe2015,
  author = {Sutcliffe, B.T.},
  title = {The quantum form of the reaction path Hamiltonian},
  journal = {Molecular Physics},
  year = {2015},
  volume = {113},
  pages = {1600-1607},
  doi = {10.1080/00268976.2014.999839}
}
Abstract: Differential cross sections (DCSs) are reported for rotationally inelastic scattering of ND3 with H2, measured using a crossed molecular beam apparatus with velocity map imaging (VMI). ND3 molecules were quantum-state selected in the ground electronic and vibrational levels and, optionally, in the j±k = 14- rotation-inversion level prior to collisions. Inelastic scattering of state-selected ND3 with H2 was measured at the mean collision energy of 580 cm-1 by resonance-enhanced multiphoton ionisation spectroscopy and VMI of ND3 in selected single final j'±k' levels. Comparison of experimental DCSs with close-coupling quantum-mechanical scattering calculations serves as a test of a recently reported ab initio potential energy surface. Calculated integral cross sections reveal the propensities for scattering into various final j'±k' levels of ND3 and differences between scattering by ortho and para H2. Integral and differential cross sections are also computed at a mean collision energy of 430 cm-1 and compared to our recent results for inelastic scattering of state-selected ND3 with He. © 2015 Taylor and Francis.
BibTeX:
@article{Tkac2015,
  author = {Tkáč, O. and Saha, A.K. and Loreau, J. and Ma, Q. and Dagdigian, P.J. and Parker, D.H. and Van Der Avoird, A. and Orr-Ewing, A.J.},
  title = {Rotationally inelastic scattering of ND 3 with H 2 as a probe of the intermolecular potential energy surface},
  journal = {Molecular Physics},
  year = {2015},
  volume = {113},
  pages = {3925-3933},
  doi = {10.1080/00268976.2015.1059958}
}
Abstract: Rotationally inelastic scattering of ND3 with Ar is studied at mean collision energies of 410 and 310 cm-1. In the experimental component of the study, ND3 molecules are prepared by supersonic expansion and subsequent hexapole state selection in the ground electronic and vibrational levels and in the jk±= 11- rotational level. A beam of state-selected ND3 molecules is crossed with a beam of Ar, and scattered ND3 molecules are detected in single final j′k′± quantum states using resonance enhanced multiphoton ionization spectroscopy. State-to-state differential cross sections for rotational-level changing collisions are obtained by velocity map imaging. The experimental measurements are compared with close-coupling quantum-mechanical scattering calculations performed using an ab initio potential energy surface. The computed DCSs agree well with the experimental measurements, confirming the high quality of the potential energy surface. The angular distributions are dominated by forward scattering for all measured final rotational and vibrational inversion symmetry states. This outcome is in contrast to our recent results for inelastic scattering of ND3 with He, where we observed significant amount of sideways and backward scattering for some final rotational levels of ND3. The differences between He and Ar collision partners are explained by differences in the potential energy surfaces that govern the scattering dynamics. © 2014 American Chemical Society.
BibTeX:
@article{Tkac2015a,
  author = {Tkáč, O. and Saha, A.K. and Loreau, J. and Parker, D.H. and Van Der Avoird, A. and Orr-Ewing, A.J.},
  title = {Rotationally Inelastic Scattering of Quantum-State-Selected ND3 with Ar},
  journal = {Journal of Physical Chemistry A},
  year = {2015},
  volume = {119},
  pages = {5979-5987},
  doi = {10.1021/jp5115042}
}
Abstract: We have recorded between 6561 and 6671 cm- 1 the spectrum of jet-cooled ammonia seeded in Ne, Ar and Kr, using continuous wave cavity ring-down spectroscopy (CW-CRDS). The equivalent absorption pathlength was around 750 m. Three bands are assigned to Π(11)←Σ(00), Π(11)←Π(10) and Δ(?)←Π(10) in the 2NH, 1+3←GS transition of the ortho NH3-Ar dimer. They are rotationally analysed and a simultaneous fitting procedure, together with one far-infrared ground state band from the literature is successfully achieved. A possible Mj-dependent cooling process is reported. Only the first of these bands is observed in the ortho NH3-Kr dimer, and rotationally analysed. Individual line perturbations and anomalous line broadening effects are reported. A J-dependent vibrational predissociation lifetime with a mean value around 0.6 ns is obtained for the Π(11) sub-state in NH3-Ar and NH3-Kr. Two additional bands are assigned to NH3-Ar involving close Π upper sub-states. A group of close bands from the para dimer is identified in NH3-Ar. The energy of all observed ortho and para sub-states is extracted from the analysis. Finally, more bands are reported but their carriers could not be identified. © 2015 Taylor and Francis.
BibTeX:
@article{Vanfleteren2015,
  author = {Vanfleteren, T. and Földes, T. and Liévin, J. and Herman, M.},
  title = {Overtone, 2NH ( 1+ 3) spectroscopy of NH 3-Ar and NH 3-Kr},
  journal = {Molecular Physics},
  year = {2015},
  volume = {113},
  pages = {3934-3945},
  doi = {10.1080/00268976.2015.1072252}
}
Abstract: The photodissociation and laser assisted dissociation of the carbon monoxide dication X3Π CO2+ into the 3Σ- states are investigated. Ab initio electronic structure calculations of the adiabatic potential energy curves, radial nonadiabatic couplings, and dipole moments for the X 3Π state are performed for 13 excited 3Σ- states of CO2+. The photodissociation cross section, calculated by time-dependent methods, shows that the C+ + O+ channels dominate the process in the studied energy range. The carbon monoxide dication CO2+ is an interesting candidate for control because it can be produced in a single, long lived, v = 0 vibrational state due to the instability of all the other excited vibrational states of the ground 3Π electronic state. In a spectral range of about 25 eV, perpendicular transition dipoles couple this 3Π state to a manifold of 3Σ- excited states leading to numerous C+ + O+ channels and a single C2+ + O channel. This unique channel is used as target for control calculations using local control theory. We illustrate the efficiency of this method in order to find a tailored electric field driving the photodissociation in a manifold of strongly interacting electronic states. The selected local pulses are then concatenated in a sequence inspired by the "laser distillation" strategy. Finally, the local pulse is compared with optimal control theory. © 2015 AIP Publishing LLC.
BibTeX:
@article{Vranckx2015,
  author = {Vranckx, S. and Loreau, J. and Vaeck, N. and Meier, C. and Desouter-Lecomte, M.},
  title = {Photodissociation of the carbon monoxide dication in the 3Σ- manifold: Quantum control simulation towards the C2+ + O channel},
  journal = {Journal of Chemical Physics},
  year = {2015},
  volume = {143},
  article number = {164309},
  doi = {10.1063/1.4934233}
}
Abstract: The Lagrange-mesh method is an approximate variational method taking the form of equations on a grid because of the use of a Gauss quadrature approximation. With a basis of Lagrange functions involving associated Laguerre polynomials related to the Gauss quadrature, the method is applied to the Dirac equation. The potential may possess a 1/r singularity. For hydrogenic atoms, numerically exact energies and wave functions are obtained with small numbers n+1 of mesh points, where n is the principal quantum number. Numerically exact mean values of powers -2 to 3 of the radial coordinate r can also be obtained with n+2 mesh points. For the Yukawa potential, a 15-digit agreement with benchmark energies of the literature is obtained with 50 or fewer mesh points. © 2014 American Physical Society.
BibTeX:
@article{Baye2014,
  author = {Baye, D. and Filippin, L. and Godefroid, M.},
  title = {Accurate solution of the Dirac equation on Lagrange meshes},
  journal = {Physical Review E - Statistical, Nonlinear, and Soft Matter Physics},
  year = {2014},
  volume = {89},
  article number = {043305},
  doi = {10.1103/PhysRevE.89.043305}
}
Abstract: We present the results of a theoretical investigation focusing on the solvent structure surrounding the -1, 0 and +1 charged species of F, Cl, Br and I halogen atoms and F2, Cl2, Br2 and I 2 di-halogen molecules in a methanol solvent and its influence on the electronic structure of the solute molecules. Our results show a large stabilizing effect arising from the solute-solvent interactions. Well-formed first solvation shells are observed for all species, the structure of which is strongly influenced by the charge of the solute species. Detailed analysis reveals that coordination number, CN, solvent orientation, and solute-solvent distance, d, are important structural characteristics which are coupled to changes in the electronic structure of the solute. We propose that the fundamental chemistry of any solute species is generally regulated by these solvent degrees of freedom. © 2014 the Owner Societies.
BibTeX:
@article{Bogatko2014,
  author = {Bogatko, S. and Cauët, E. and Geerlings, P. and De Proft, F.},
  title = {On the coupling of solvent characteristics to the electronic structure of solute molecules},
  journal = {Physical Chemistry Chemical Physics},
  year = {2014},
  volume = {16},
  pages = {3807-3814},
  doi = {10.1039/c3cp54944e}
}
Abstract: The first quantitative description of the Rydberg and valence singlet electronic states of vinylidene lying in the 0-10 eV region is performed by using large scale ab initio calculations. A deep analysis of Rydberg-valence interactions has been achieved thanks to the comprehensive information contained in the accurate Multi-Reference Configuration Interaction wavefunctions and an original population analysis highlighting the respective role played by orbital and state mixing in such interactions. The present theoretical approach is thus adequate for dealing with larger than diatomic Rydberg systems. The nine lowest singlet valence states have been optimized. Among them, some are involved in strong Rydberg-valence interactions in the region of the Rydberg state equilibrium geometry. The Rydberg states of vinylidene present a great similarity with the acetylene isomer, concerning their quantum defects and Rydberg molecular orbital character. As in acetylene, strong s-d mixing is revealed in the n = 3 s-d supercomplex. Nevertheless, unlike in acetylene, the close-energy of the two vinylidene ionic cores 2A1 and 2B1 results into two overlapped Rydberg series. These Rydberg series exhibit local perturbations when an accidental degeneracy occurs between them and results in avoided crossings. In addition, some Δl = 1 (s-p and p-d) mixings arise for some Rydberg states and are rationalized in term of electrostatic interaction from the electric dipole moment of the ionic core. The strongest dipole moment of the 2 B1 cationic state also stabilizes the lowest members of the n = 3 Rydberg series converging to this excited state, as compared to the adjacent series converging toward the 2A1 ionic ground state. The overall energies of vinylidene Rydberg states lie above their acetylene counterpart. Finally, predictions for optical transitions in singlet vinylidene are suggested for further experimental spectroscopic characterization of vinylidene. © 2014 AIP Publishing LLC.
BibTeX:
@article{Boye-Peronne2014,
  author = {Boyé-Péronne, S. and Gauyacq, D. and Liévin, J.},
  title = {Theoretical description of electronically excited vinylidene up to 10 eV: First high level ab initio study of singlet valence and Rydberg states},
  journal = {Journal of Chemical Physics},
  year = {2014},
  volume = {141},
  article number = {174317},
  doi = {10.1063/1.4900875}
}
Abstract: The isotope effects in Si- bound levels are studied using the multiconfiguration Hartree-Fock ab initio approach. Large-scale calculations are carried out for the 3p34So, 2Do, and 2Po multiplets of Si- and the 3p23P multiplet of Si. We predict an anomalous isotope shift on the electron affinity, dominated by the specific mass shift, with a value of -0.66(6) m-1 for the 30-28 isotope pair. We also report hyperfine-structure parameters for the studied multiplets. We provide the values of level electric-field gradients at the nucleus that could be of interest in a study of the metastable silicon isotopes. Relativistic corrections are estimated using nonrelativistic orbitals in the Breit-Pauli and fully relativistic frameworks. © 2014 American Physical Society.
BibTeX:
@article{Carette2014,
  author = {Carette, T. and Godefroid, M.R.},
  title = {Theoretical study of the isotope effects on the detachment thresholds of Si-},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2014},
  volume = {89},
  article number = {052513},
  doi = {10.1103/PhysRevA.89.052513}
}
Abstract: Extensive self-consistent multiconfiguration Dirac-Hartree-Fock (MCDHF) calculations and subsequent relativistic configuration interaction calculations are performed for 262 states belonging to the 15 configurations 2s 22p2, 2s2p3, 2p4, 2s 22p3l, 2s2p23l, 2p33l and 2s22p4l(l = 0,1,2) in selected carbon-like ions from Ar XIII to Zn XXV. Electron correlation effects are accounted for through large configuration state function expansions. Calculated energy levels are compared with existing theoretical calculations and data from the Chianti and NIST databases. In addition, Landé gJ-factors and radiative electric dipole transition rates are given for all ions. The accuracy of the calculations are high enough to facilitate the identification of observed spectral lines. © 2014 ESO.
BibTeX:
@article{Ekman2014,
  author = {Ekman, J. and Jönsson, P. and Gustafsson, S. and Hartman, H. and Gaigalas, G. and Godefroid, M.R. and Froese Fischer, C.},
  title = {Calculations with spectroscopic accuracy: Energies, transition rates,and Lande gJ-factors in the carbon isoelectronic sequence from Ar XIII to Zn XXV},
  journal = {Astronomy and Astrophysics},
  year = {2014},
  volume = {564},
  article number = {A24},
  doi = {10.1051/0004-6361/201323163}
}
Abstract: Relativistic dipolar to hexadecapolar polarizabilities of the ground state and some excited states of hydrogenic atoms are calculated by using numerically exact energies and wave functions obtained from the Dirac equation with the Lagrange-mesh method. This approach is an approximate variational method taking the form of equations on a grid because of the use of a Gauss quadrature approximation. The partial polarizabilities conserving the absolute value of the quantum number κ are also numerically exact with small numbers of mesh points. The ones where |κ| changes are very accurate when using three different meshes for the initial and final wave functions and for the calculation of matrix elements. The polarizabilities of the n=2 excited states of hydrogenic atoms are also studied with a separate treatment of the final states that are degenerate at the nonrelativistic approximation. The method provides high accuracies for polarizabilities of a particle in a Yukawa potential and is applied to a hydrogen atom embedded in a Debye plasma. © 2014 American Physical Society.
BibTeX:
@article{Filippin2014,
  author = {Filippin, L. and Godefroid, M. and Baye, D.},
  title = {Relativistic polarizabilities with the Lagrange-mesh method},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2014},
  volume = {90},
  article number = {052520},
  doi = {10.1103/PhysRevA.90.052520}
}
Abstract: The electronic structure of DNA is determined by its nucleotide sequence, which is for instance exploited in molecular electronics. Here we demonstrate that also the DNA strand breakage induced by low-energy electrons (18 eV) depends on the nucleotide sequence. To determine the absolute cross sections for electron induced single strand breaks in specific 13 mer oligonucleotides we used atomic force microscopy analysis of DNA origami based DNA nanoarrays. We investigated the DNA sequences 5′-TT(XYX) 3 TT with X = A, G, C and Y = T, BrU 5-bromouracil and found absolute strand break cross sections between 2.66 · 10-14 cm2 and 7.06 · 10-14 cm2. The highest cross section was found for 5 2-TT(ATA) 3 TT and 5 2-TT(ABrUA) 3 TT, respectively. BrU is a radiosensitizer, which was discussed to be used in cancer radiation therapy. The replacement of T by BrU into the investigated DNA sequences leads to a slight increase of the absolute strand break cross sections resulting in sequence-dependent enhancement factors between 1.14 and 1.66. Nevertheless, the variation of strand break cross sections due to the specific nucleotide sequence is considerably higher. Thus, the present results suggest the development of targeted radiosensitizers for cancer radiation therapy.
BibTeX:
@article{Keller2014,
  author = {Keller, A. and Rackwitz, J. and Cauët, E. and Liévin, J. and Körzdörfer, T. and Rotaru, A. and Gothelf, K.V. and Besenbacher, F. and Bald, I.},
  title = {Sequence dependence of electron-induced DNA strand breakage revealed by DNA nanoarrays},
  journal = {Scientific Reports},
  year = {2014},
  volume = {4},
  article number = {7391},
  doi = {10.1038/srep07391}
}
Abstract: We illustrate computational aspects of the calculation of the potential energy surfaces of small (up to five atoms) van der Waals complexes with high-level quantum chemistry techniques such as the CCSD(T) method with extended basis sets. We discuss the compromise between the required accuracy and the computational time. Further, we show how these potential energy surfaces can be fitted and used in dynamical calculations such as non-reactive inelastic scattering. © 2014 AIP Publishing LLC.
BibTeX:
@conference{Loreau2014b,
  author = {Loreau, J.},
  title = {Structure and dynamics of small van der Waals complexes},
  journal = {AIP Conference Proceedings},
  year = {2014},
  volume = {1618},
  pages = {585-588},
  doi = {10.1063/1.4897805}
}
Abstract: A new, four-dimensional potential energy surface for the interaction of NH3 and ND3 with Ar is computed using the coupled-cluster method with single, double, and perturbative triple excitations and large basis sets. The umbrella motion of the ammonia molecule is explicitly taken into account. The bound states of both NH3-Ar and ND3-Ar are calculated on this potential for total angular momentum values from J = 0 to 10, with the inclusion of Coriolis interactions. The energies and splittings of the rovibrational levels are in excellent agreement with the extensive high-resolution spectroscopic data accumulated over the years in the infrared and microwave regions for both complexes, which demonstrates the quality of the potential energy surface. © 2014 AIP Publishing LLC.
BibTeX:
@article{Loreau2014,
  author = {Loreau, J. and Liévin, J. and Scribano, Y. and Van Der Avoird, A.},
  title = {Potential energy surface and bound states of the NH3-Ar and ND3-Ar complexes},
  journal = {Journal of Chemical Physics},
  year = {2014},
  volume = {141},
  article number = {224303},
  doi = {10.1063/1.4903047}
}
Abstract: The cross section for charge transfer in proton-helium collisions has been computed in the energy range from 10eV/u up to 10 MeV/u. Four different methods (full quantal time-independent and time-dependent methods, molecular and atomic basis set semi-classical approaches) valid in different energy regimes have been used to calculate the partial and total cross section for single-electron capture. The results are compared with previous theoretical calculations and experimental measurements and the different theoretical methods used are shown to be complementary for describing the charge transfer reaction. A fit of the cross section, valid for collision energies from 10eV/u up to 10 MeV/u is presented based on these results. © 2014 IOP Publishing Ltd.
BibTeX:
@article{Loreau2014a,
  author = {Loreau, J. and Ryabchenko, S. and Vaeck, N.},
  title = {Charge transfer in proton-helium collisions from low to high energy},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2014},
  volume = {47},
  article number = {135204},
  doi = {10.1088/0953-4075/47/13/135204}
}
Abstract: The advent of high-resolution spectrographs and detailed stellar atmosphere modelling has strengthened the need for accurate molecular data. Carbon-enhanced metal-poor (CEMP) stars spectra are interesting objects with which to study transitions from the CH molecule. We combine programs for spectral analysis of molecules and stellar-radiative transfer codes to build an extensive CH linelist, including predissociation broadening as well as newly identified levels. We show examples of strong predissociation CH lines in CEMP stars, and we stress the important role played by the CH features in the Bond-Neff feature depressing the spectra of barium stars by as much as 0.2 mag in the λ = 3000-5500 Å range. Because of the extreme thermodynamic conditions prevailing in stellar atmospheres (compared to the laboratory), molecular transitions with high energy levels can be observed. Stellar spectra can thus be used to constrain and improve molecular data. © 2014 ESO.
BibTeX:
@article{Masseron2014,
  author = {Masseron, T. and Plez, B. and Van Eck, S. and Colin, R. and Daoutidis, I. and Godefroid, M. and Coheur, P.-F. and Bernath, P. and Jorissen, A. and Christlieb, N.},
  title = {CH in stellar atmospheres: An extensive linelist},
  journal = {Astronomy and Astrophysics},
  year = {2014},
  volume = {571},
  article number = {A47},
  doi = {10.1051/0004-6361/201423956}
}
Abstract: Energy levels, normal and specific mass shift parameters as well as electronic densities at the nucleus are reported for numerous states along the beryllium, boron, carbon, and nitrogen isoelectronic sequences. Combined with nuclear data, these electronic parameters can be used to determine values of level and transition isotope shifts. The calculation of the electronic parameters is done using first-order perturbation theory with relativistic configuration interaction wavefunctions that account for valence, core-valence, and core-core correlation effects as zero-order functions. Results are compared with experimental and other theoretical values, when available. © 2014 Elsevier Inc.
BibTeX:
@article{Naze2014,
  author = {Nazé, C. and Verdebout, S. and Rynkun, P. and Gaigalas, G. and Godefroid, M. and Jönsson, P.},
  title = {Isotope shifts in beryllium-, boron-, carbon-, and nitrogen-like ions from relativistic configuration interaction calculations},
  journal = {Atomic Data and Nuclear Data Tables},
  year = {2014},
  volume = {100},
  pages = {1197-1249},
  doi = {10.1016/j.adt.2014.02.004}
}
Abstract: We assess the pros and cons of a large panel of DFT exchange-correlation functionals for the prediction of the electronic structure of hydrogen-rich peptide radicals formed after electron attachment on a protonated peptide. Indeed, despite its importance in the understanding of the chemical changes associated with the reduction step, the question of the attachment site of an electron and, more generally, of the reduced species formed in the gas phase through electron-induced dissociation (ExD) processes in mass spectrometry is still a matter of debate. For hydrogen-rich peptide radicals in which several positive groups and low-lying π* orbitals can capture the incoming electron in ExD, inclusion of full Hartree-Fock exchange at long-range interelectronic distance is a prerequisite for an accurate description of the electronic states, thereby excluding several popular exchange-correlation functionals, e.g., B3LYP, M06-2X, or CAM-B3LYP. However, we show that this condition is not sufficient by comparing the results obtained with asymptotically correct range-separated hybrids (M11, LC-BLYP, LC-BPW91, ωB97, ωB97X, and ωB97X-D) and with reference CASSCF-MRCI and EOM-CCSD calculations. The attenuation parameter ω significantly tunes the spin density distribution and the excited states vertical energies. The investigated model structures, ranging from methylammonium to hexapeptide, allow us to obtain a description of the nature and energy of the electronic states, depending on (i) the presence of hydrogen bond(s) around the cationic site(s), (ii) the presence of π* molecular orbitals (MOs), and (iii) the selected DFT approach. It turns out that, in the present framework, LC-BLYP and ωB97 yields the most accurate results. © 2014 American Chemical Society.
BibTeX:
@article{Riffet2014,
  author = {Riffet, V. and Jacquemin, D. and Cauët, E. and Frison, G.},
  title = {Benchmarking DFT and TD-DFT functionals for the ground and excited states of hydrogen-rich peptide radicals},
  journal = {Journal of Chemical Theory and Computation},
  year = {2014},
  volume = {10},
  pages = {3308-3318},
  doi = {10.1021/ct5004912}
}
Abstract: We investigate the interaction of ground and excited states of silver atom with all the noble gases, including helium. Born-Oppenheimer potential energy curves are calculated with quantum chemical techniques and spin-orbit effects in the excited states are included. We compare with experimentally available spectroscopic data, as well as previous calculations. The assignment of vibrational levels in the one experiment we compare with, may have to shift up by one unit. © Published under licence by IOP Publishing Ltd.
BibTeX:
@article{Sadeghpour2014,
  author = {Sadeghpour, H.R. and Loreau, J. and Dalgarno, A.},
  title = {Interaction of Ag(5s) and Ag(5p) with noble gas atoms},
  journal = {Journal of Physics: Conference Series},
  year = {2014},
  volume = {488},
  article number = {122006},
  doi = {10.1088/1742-6596/488/12/122006}
}
Abstract: The constraint of time-integrated zero area on the laser field is a fundamental requirement, both theoretically and experimentally, in the control of molecular dynamics. By using techniques of local and optimal control theory, we show how to enforce this constraint in two benchmark control problems, namely, molecular orientation and photofragmentation. The origin and the physical implications for the dynamics of this zero-area control field are discussed. © 2014 American Physical Society.
BibTeX:
@article{Sugny2014,
  author = {Sugny, D. and Vranckx, S. and Ndong, M. and Vaeck, N. and Atabek, O. and Desouter-Lecomte, M.},
  title = {Control of molecular dynamics with zero-area fields: Application to molecular orientation and photofragmentation},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2014},
  volume = {90},
  article number = {053404},
  doi = {10.1103/PhysRevA.90.053404}
}
Abstract: In our previous paper [B. T. Sutcliffe and R. G. Woolley, J. Chem. Phys. 137, 22A544 (2012)] we argued that the Born-Oppenheimer approximation could not be based on an exact transformation of the molecular Schrödinger equation. In this Comment we suggest that the fundamental reason for the approximate nature of the Born-Oppenheimer model is the lack of a complete set of functions for the electronic space, and the need to describe the continuous spectrum using spectral projection. © 2014 AIP Publishing LLC.
BibTeX:
@article{Sutcliffe2014,
  author = {Sutcliffe, B.T. and Woolley, R.G.},
  title = {Comment on "on the quantum theory of molecules" [J. Chem. Phys. 137, 22A544 (2012)]},
  journal = {Journal of Chemical Physics},
  year = {2014},
  volume = {140},
  article number = {4861897},
  doi = {10.1063/1.4861897}
}
Abstract: Energy levels, hyperfine interaction constants, and Landé gJ-factors are reported for n=2 states in beryllium-, boron-, carbon-, and nitrogen-like ions from relativistic configuration interaction calculations. Valence, core-valence, and core-core correlation effects are taken into account through single and double-excitations from multireference expansions to increasing sets of active orbitals. A systematic comparison of the calculated hyperfine interaction constants is made with values from the available literature. © 2014 Elsevier Inc.
BibTeX:
@article{Verdebout2014,
  author = {Verdebout, S. and Nazé, C. and Jönsson, P. and Rynkun, P. and Godefroid, M. and Gaigalas, G.},
  title = {Hyperfine structures and Landé gJ-factors for n=2 states in beryllium-, boron-, carbon-, and nitrogen-like ions from relativistic configuration interaction calculations},
  journal = {Atomic Data and Nuclear Data Tables},
  year = {2014},
  volume = {100},
  pages = {1111-1155},
  doi = {10.1016/j.adt.2014.05.001}
}
Abstract: A new method for the synthesis of 15N-labeled chiral β-diamines from a common precursor, either optically pure amino acids or anti-β-amino alcohols, is reported. The two diastereomeric series of vicinal diamines are produced through the nucleophilic ring opening of activated chiral aziridines. 15N was introduced by means of [ 15N]-benzylamine, prepared from 15NH4Cl. The final compounds are highly valuable because [1H-15N] NMR is considered a powerful tool for studying the chemical properties of platinum-based complexes. © 2012 Published by Elsevier Ltd.
BibTeX:
@article{Berger2013,
  author = {Berger, G. and Gelbcke, M. and Cauët, E. and Luhmer, M. and Nève, J. and Dufrasne, F.},
  title = {Synthesis of 15N-labeled vicinal diamines through N-activated chiral aziridines: Tools for the NMR study of platinum-based anticancer compounds},
  journal = {Tetrahedron Letters},
  year = {2013},
  volume = {54},
  pages = {545-548},
  doi = {10.1016/j.tetlet.2012.11.079}
}
Abstract: Herein, we report on the structure and dynamics of the aqueous Ca 2+ system studied by using ab initio molecular dynamics (AIMD) simulations. Our detailed study revealed the formation of well-formed hydration shells with characteristics that were significantly different to those of bulk water. To facilitate a robust comparison with state-of-the-art X-ray absorption fine structure (XAFS) data, we employ a 1st principles MD-XAFS procedure and directly compare simulated and experimental XAFS spectra. A comparison of the data for the aqueous Ca2+ system with those of the recently reported Zn2+, Fe3+, and Al3+ species showed that many of their structural characteristics correlated well with charge density on the cation. Some very important exceptions were found, which indicated a strong sensitivity of the solvent structure towards the cation′s valence electronic structure. Average dipole moments for the 2nd shell of all cations were suppressed relative to bulk water. Like a duck to water: An investigation into the solvent structure and dynamics around the Ca2+ cation was validated by comparison with XAFS data. A comparison with ab initio molecular dynamics studies of aqueous Zn2+, Fe3+, and Al 3+ was used to discuss general trends in the ability of these solvated cations to form extended structures. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
BibTeX:
@article{Bogatko2013b,
  author = {Bogatko, S. and Cauët, E. and Bylaska, E. and Schenter, G. and Fulton, J. and Weare, J.},
  title = {The aqueous Ca2+ system, in comparison with Zn2+, Fe3 +, and Al3 +: An ab initio molecular dynamics study},
  journal = {Chemistry - A European Journal},
  year = {2013},
  volume = {19},
  pages = {3047-3060},
  doi = {10.1002/chem.201202821}
}
Abstract: We present results showing that our recently developed density functional theory (DFT)-based speciation model of the aqueous Al3+ system has the potential to improve the interpretations of ESI-MS studies of aqueous metal cation hydrolytic speciation. The main advantages of our method are that (1) it allows for the calculation of the relative abundance of a given species which may be directly assigned to the signal intensity in a mass spectrum; (2) in cases where species with identical m/z ratios may coexist, the assignment can be unambiguously assigned based on their theoretical relative abundances. As a demonstration of its application, we study four pairs of monomer and dimer aqueous Al3+ species, each with identical m/z ratio. For some of these pairs our method predicts that the dominant species changes from the monomer to the dimer species under varying pH conditions. [Figure not available: see fulltext.] © 2013 American Society for Mass Spectrometry.
BibTeX:
@article{Bogatko2013a,
  author = {Bogatko, S. and Cauët, E. and Geerlings, P.},
  title = {Improved DFT-based interpretation of ESI-MS of aqueous metal cations},
  journal = {Journal of the American Society for Mass Spectrometry},
  year = {2013},
  volume = {24},
  pages = {926-931},
  doi = {10.1007/s13361-013-0617-x}
}
Abstract: We predict that electron attachment may be used with ESI-MS techniques to observe neutral Al metal aqua-oxo-hydroxo species and the complex polymerization and precipitation reactions in which they participate. Neutral aqueous metal species have, so far, been invisible to ESI-MS techniques. This journal is © 2013 the Owner Societies.
BibTeX:
@article{Bogatko2013,
  author = {Bogatko, S. and Cauët, E. and Geerlings, P.},
  title = {Rydberg electron capture by neutral Al hydrolysis products},
  journal = {Physical Chemistry Chemical Physics},
  year = {2013},
  volume = {15},
  pages = {15309-15311},
  doi = {10.1039/c3cp51935j}
}
Abstract: Today, the electron affinity is experimentally well known for most of the elements and is a useful guideline for developing ab initio computational methods. However, the measurements of isotope shifts on the electron affinity are limited by both resolution and sensitivity. In this context, theory is of great help to further our knowledge and understanding of atomic structures, even though correlation plays a dominant role in negative ions' properties and, particularly, in the calculation of the specific mass shift contribution. This study solves the longstanding discrepancy between calculated and measured specific mass shifts on the electron affinity of chlorine (Berzinsh et al 1995 Phys. Rev. A 51 231). © 2013 IOP Publishing Ltd.
BibTeX:
@article{Carette2013,
  author = {Carette, T. and Godefroid, M.R.},
  title = {Isotope shift on the chlorine electron affinity revisited by an MCHF/CI approach},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2013},
  volume = {46},
  article number = {095003},
  doi = {10.1088/0953-4075/46/9/095003}
}
Abstract: The hyperfine interaction constants of the 2p4(3P)3p 2D3/2,5/2o, 4D1/2-7/2o, and 4P1/2-5/2o levels in neutral fluorine are investigated theoretically. Large-scale calculations are carried out using the multiconfiguration Hartree-Fock (MCHF) and Dirac-Hartree-Fock (MCDHF) methods. In the framework of the MCHF approach, the relativistic effects are taken into account in the Breit-Pauli approximation using nonrelativistic orbitals. In the fully relativistic approach, the orbitals are optimized using the Dirac-Coulomb Hamiltonian with correlation models inspired by the nonrelativistic calculations. Higher-order excitations are captured through multireference configuration interaction calculations including the Breit interaction. In a third (intermediate) approach, the Dirac-Coulomb-Breit Hamiltonian matrix is diagonalized in a relativistic configuration space built with nonrelativistic MCHF radial functions converted into Dirac spinors using the Pauli approximation. The magnetic dipole hyperfine-structure constants calculated with the three relativistic models are consistent and reveal unexpectedly large effects of relativity for 2D5/2o, 4P3/2o, and 4P5/2o. The agreement with the few available experimental values is satisfactory. The strong J dependence of relativistic corrections on the hyperfine constants is investigated through the detailed analysis of the orbital, spin-dipole, and contact relative contributions calculated with the nonrelativistic magnetic dipole operator. © 2013 American Physical Society.
BibTeX:
@article{Carette2013a,
  author = {Carette, T. and Nemouchi, M. and Li, J. and Godefroid, M.},
  title = {Relativistic effects on the hyperfine structures of 2p4(3P) 3p2Do,4Do, and 4Po in 19F i},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2013},
  volume = {88},
  article number = {042501},
  doi = {10.1103/PhysRevA.88.042501}
}
Abstract: In a previous article a dipole moment surface (DMS) of full-electron, multi-reference configuration interaction (MRCI) quality was obtained and used to calculate the rotational spectrum of methane vibrational ground state, by means of a combination of the mean field configuration interaction method (VMFCI) with a generalized perturbation theory. The theoretical line intensities were matching the experimental ones obtained at the SOLEIL synchrotron well within experimental uncertainties. However, not all third order terms were included in this DMS. In the present work, additional DMS points have been calculated and fitted using a complete third order expansion. The new results give R-branch intensities systematically smaller by about 1% compared to those previously obtained by using the same ab initio method, so still within experimental errors. The relevance of this DMS to calculate intensities for excited vibrational states, in particular for the dyad, is addressed. © 2013 Elsevier Inc. All rights reserved.
BibTeX:
@article{Cassam-Chenai2013,
  author = {Cassam-Chenaï, P. and Liévin, J.},
  title = {An improved third order dipole moment surface for methane},
  journal = {Journal of Molecular Spectroscopy},
  year = {2013},
  volume = {291},
  pages = {77-84},
  doi = {10.1016/j.jms.2013.07.004}
}
Abstract: Low energy electron-attachment-induced damage in DNA, where dissociation channels may involve multiple bonds including complex bond rearrangements and significant nuclear motions, is analyzed here. Quantum mechanics/molecular mechanics (QM/MM) calculations reveal how rearrangements of electron density after vertical electron attachment modulate the position and dynamics of the atomic nuclei in DNA. The nuclear motions involve the elongation of the P-O (P-O3′ and P-O5′) and C-C (C3′-C4′ and C4′-C5′) bonds for which the acquired kinetic energy becomes high enough so that the neighboring C3′-O3′ or C5′-O5′ phosphodiester bond may break almost immediately. Such dynamic behavior should happen on a very short time scale, within 15-30 fs, which is of the same order of magnitude as the time scale predicted for the excess electron to localize around the nucleobases. This result indicates that the C-O phosphodiester bonds can break before electron transfer from the backbone to the base. © 2013 American Chemical Society.
BibTeX:
@article{Cauet2013,
  author = {Cauët, E. and Bogatko, S. and Liévin, J. and De Proft, F. and Geerlings, P.},
  title = {Electron-attachment-induced DNA damage: Instantaneous strand breaks},
  journal = {Journal of Physical Chemistry B},
  year = {2013},
  volume = {117},
  pages = {9669-9676},
  doi = {10.1021/jp406320g}
}
Abstract: No lines have been observed for transitions between the doublet and quartet levels of B i. Consequently, energy levels based on observation for the latter are obtained through extrapolation of wavelengths along the isoelectronic sequence for the 2s22p 2P3/2o - 2s2p2 4P5/2 transition. In this paper, accurate theoretical excitation energies from a partitioned-correlation- function-interaction (PCFI) method are reported for B i that include both relativistic effects in the Breit-Pauli approximation and a finite mass correction. Results are compared with extrapolated values from observed data. For B i our estimate of the excitation energy 28 959 ± 5 cm-1 is in better agreement with the values obtained by Edlén (1969) than those reported by Kramida and Ryabtsev (2007). Our method is validated by applying the same procedure to the separation of these levels in C ii. © 2013 American Physical Society.
BibTeX:
@article{FroeseFischer2013,
  author = {Froese Fischer, C. and Verdebout, S. and Godefroid, M. and Rynkun, P. and Jönsson, P. and Gaigalas, G.},
  title = {Doublet-quartet energy separation in boron: A partitioned-correlation- function-interaction method},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2013},
  volume = {88},
  article number = {062506},
  doi = {10.1103/PhysRevA.88.062506}
}
Abstract: Relativistic configuration interaction (RCI) calculations are performed for 291 states belonging to the configurations 1s22s22p, 1s22s2p2, 1s22p3, 1s 22s23l, 1s22s2p3l, 1s22p 23l, 1s22s24l′, 1s 22s2p4l′, and 1s22p24l′ (l = 0,1,2 and l′ = 0,1,2,3) in boron-like ions Si X and Ti XVIII to Cu XXV. Electron correlation effects are represented in the wave functions by large configuration state function (CSF) expansions. States are transformed from jj-coupling to LS-coupling, and the LS-percentage compositions are used for labeling the levels. Radiative electric dipole transition rates are given for all ions, leading to massive data sets. Calculated energy levels are compared with other theoretical predictions and crosschecked against the Chianti database, NIST recommended values, and other observations. The accuracy of the calculations are high enough to facilitate the identification of observed spectral lines. © 2013 ESO.
BibTeX:
@article{Joensson2013,
  author = {Jönsson, P. and Ekman, J. and Gustafsson, S. and Hartman, H. and Karlsson, L.B. and Du Rietz, R. and Gaigalas, G. and Godefroid, M.R. and Froese Fischer, C.},
  title = {Energy levels and transition rates for the boron isoelectronic sequence: Si X, Ti XVIII-Cu XXV},
  journal = {Astronomy and Astrophysics},
  year = {2013},
  volume = {559},
  article number = {A100},
  doi = {10.1051/0004-6361/201321893}
}
Abstract: The development of multiconfiguration computer packages for atomic structure calculations is reviewed with special attention to the work of Charlotte Froese Fischer. The underlying theory is described along with methodologies to choose basis expansions of configuration state functions. Calculations of energies and transitions rates are presented and the accuracy of the results is assessed. Limitations of multiconfiguration methods are discussed and it is shown how these limitations can be circumvented by a division of the original large-scale computational problem into a number of smaller problems. © 2013 AIP Publishing LLC.
BibTeX:
@conference{Joensson2013a,
  author = {Jönsson, P. and Godefroid, M. and Gaigalas, G. and Bieroń, J. and Brage, T.},
  title = {Accurate transition probabilities from large-scale multiconfiguration calculations - A tribute to Charlotte Froese Fischer},
  journal = {AIP Conference Proceedings},
  year = {2013},
  volume = {1545},
  pages = {266-278},
  doi = {10.1063/1.4815863}
}
Abstract: The high-resolution infrared spectra of the ν1 + ν3 (2CH) band of the Ar-C2H2 complex has been recorded from 6544 to 6566 cm-1. The previously reported K a = 1 ← 0, 2 ← 1, and 0 ← 1 subbands were observed and the Ka = 1 ← 2, 2 ← 3, and 3 ← 2 subbands were assigned for the first time. The intermolecular potential energy surface of this complex has been calculated ab initio and optimized by fitting the new high-resolution data. Refined intermolecular potential energy surfaces have been obtained for the ground vibrational state and for the excited v1 = v3 = 1 stretching state. For the former state, the results of the analysis are satisfactory and the microwave transitions of the complex are reproduced with a root-mean-square deviation of 5 MHz. For the latter state, systematic discrepancies arise in the analysis. © 2013 American Chemical Society.
BibTeX:
@article{Lauzin2013,
  author = {Lauzin, C. and Coudert, L.H. and Herman, M. and Liévin, J.},
  title = {Ab initio intermolecular potential of Ar-C2H2 refined using high-resolution spectroscopic data},
  journal = {Journal of Physical Chemistry A},
  year = {2013},
  volume = {117},
  pages = {13767-13774},
  doi = {10.1021/jp408013n}
}
Abstract: We calculate the index of refraction of sodium matter waves propagating through a gas of nitrogen molecules. We use a recent ab initio potential for the ground state of the NaN2 van der Waals complex to perform quantal close-coupling calculations and compute the index of refraction as a function of the projectile velocity. We obtain good agreement with the available experimental data. We show that the refractive index contains glory oscillations but that they are damped by the averaging over the thermal motion of the N 2 molecules. These oscillations appear at lower temperatures and projectile velocity. We also investigate the behavior of the refractive index at low temperature and low projectile velocity to show its dependence on the rotational state of N2 and discuss the advantage of using diatomic molecules as projectiles. © 2013 American Physical Society.
BibTeX:
@article{Loreau2013,
  author = {Loreau, J. and Kharchenko, V. and Dalgarno, A.},
  title = {Index of refraction of molecular nitrogen for sodium matter waves},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2013},
  volume = {87},
  article number = {012708},
  doi = {10.1103/PhysRevA.87.012708}
}
Abstract: We investigate the interaction of ground and excited states of a silver atom with noble gases (NG), including helium. Born-Oppenheimer potential energy curves are calculated with quantum chemistry methods and spin-orbit effects in the excited states are included by assuming a spin-orbit splitting independent of the internuclear distance. We compare our results with experimentally available spectroscopic data, as well as with previous calculations. Because of strong spin-orbit interactions, excited Ag-NG potential energy curves cannot be fitted to Morse-like potentials. We find that the labeling of the observed vibrational levels has to be shifted by one unit. © 2013 American Institute of Physics.
BibTeX:
@article{Loreau2013b,
  author = {Loreau, J. and Sadeghpour, H.R. and Dalgarno, A.},
  title = {Potential energy curves for the interaction of Ag(5s) and Ag(5p) with noble gas atoms},
  journal = {Journal of Chemical Physics},
  year = {2013},
  volume = {138},
  article number = {084301},
  doi = {10.1063/1.4790586}
}
Abstract: We investigate the photodissociation of HeH+ in the metastable triplet state as well as its formation through the inverse process, radiative association. In models of astrophysical plasmas, HeH+ is assumed to be present only in the ground state, and the influence of the triplet state has not been explored. It may be formed by radiative association during collisions between a proton and metastable helium, which are present in significant concentrations in nebulae. The triplet state can also be formed by association of He+ and H, although this process is less likely to occur. We compute the cross sections and rate coefficients corresponding to the photodissociation of the triplet state by UV photons from a central star using a wave packet method. We show that the photodissociation cross sections depend strongly on the initial vibrational state and that the effects of excited electronic states and nonadiabatic couplings cannot be neglected. We then calculate the cross section and rate coefficient for the radiative association of HeH+ in the metastable triplet state. © 2013 American Chemical Society.
BibTeX:
@article{Loreau2013a,
  author = {Loreau, J. and Vranckx, S. and Desouter-Lecomte, M. and Vaeck, N. and Dalgarno, A.},
  title = {Photodissociation and radiative association of HeH+ in the metastable triplet state},
  journal = {Journal of Physical Chemistry A},
  year = {2013},
  volume = {117},
  pages = {9486-9492},
  doi = {10.1021/jp312007q}
}
Abstract: An atomic spectral line is characteristic of the element producing the spectrum. The line also depends on the isotope. The program ris3 (Relativistic Isotope Shift) calculates the electron density at the origin and the normal and specific mass shift parameters. Combining these electronic quantities with available nuclear data, isotope-dependent energy level shifts are determined. © 2013 Elsevier B.V. All rights reserved.
BibTeX:
@article{Naze2013,
  author = {Nazé, C. and Gaidamauskas, E. and Gaigalas, G. and Godefroid, M. and Jönsson, P.},
  title = {Ris3: A program for relativistic isotope shift calculations},
  journal = {Computer Physics Communications},
  year = {2013},
  volume = {184},
  pages = {2187-2196},
  doi = {10.1016/j.cpc.2013.02.015}
}
Abstract: In view of preparing Cu polynuclear complexes with dipyrromethene ligands, the mononuclear complexes [Cu(ii)(dipy)2] (dipyH = 5-phenyldipyrromethene) and [Cu(ii)(dpdipy)2] (dpdipyH = 1,5,9-triphenyldipyrromethene) have been prepared and characterized by X-ray crystallography, mass spectrometry and EPR spectroscopy. Their peculiar redox and spectroscopic (absorption/emission) behaviours are discussed. In contrast to CuII complexes of 1,1′-bidypyrrin, the reduction electrolysis of [Cu(ii)(dpdipy)2] leads to decomposition products on a time scale of a few hours. Moreover in relation to this observation, [Cu(i)(dpdipy) 2]- could not be synthesized in spite of the Cu I core protection by the phenyl substituents in ortho position of the nitrogen atoms. Theoretical calculations provide some explanations for this instability. Interestingly [Cu(ii)(dipy)2] and [Cu(ii)(dpdipy) 2] display weak luminescence at room temperature, attributed to a ligand centered emission. © 2013 The Royal Society of Chemistry.
BibTeX:
@article{Servaty2013,
  author = {Servaty, K. and Cauët, E. and Thomas, F. and Lambermont, J. and Gerbaux, P. and De Winter, J. and Ovaere, M. and Volker, L. and Vaeck, N. and Van Meervelt, L. and Dehaen, W. and Moucheron, C. and Kirsch-De Mesmaeker, A.},
  title = {Peculiar properties of homoleptic Cu complexes with dipyrromethene derivatives},
  journal = {Dalton Transactions},
  year = {2013},
  volume = {42},
  pages = {14188-14199},
  doi = {10.1039/c3dt51541a}
}
Abstract: The traditional multiconfiguration Hartree-Fock (MCHF) and configuration interaction (CI) methods are based on a single orthonormal orbital basis. For atoms with many closed core shells, or complicated shell structures, a large orbital basis is needed to saturate the different electron correlation effects such as valence, core-valence and correlation within the core shells. The large orbital basis leads to massive configuration state function (CSF) expansions that are difficult to handle, even on large computer systems. We show that it is possible to relax the orthonormality restriction on the orbital basis and break down the originally very large calculations into a series of smaller calculations that can be run in parallel. Each calculation determines a partitioned correlation function (PCF) that accounts for a specific correlation effect. The PCFs are built on optimally localized orbital sets and are added to a zero-order multireference (MR) function to form a total wave function. The expansion coefficients of the PCFs are determined from a low dimensional generalized eigenvalue problem. The interaction and overlap matrices are computed using a biorthonormal transformation technique (Verdebout et al 2010 J. Phys. B: At. Mol. Phys. 43 074017). The new method, called partitioned correlation function interaction (PCFI), converges rapidly with respect to the orbital basis and gives total energies that are lower than the ones from ordinary MCHF and CI calculations. The PCFI method is also very flexible when it comes to targeting different electron correlation effects. Focusing our attention on neutral lithium, we show that by dedicating a PCF to the single excitations from the core, spin- and orbital-polarization effects can be captured very efficiently, leading to highly improved convergence patterns for hyperfine parameters compared with MCHF calculations based on a single orthogonal radial orbital basis. By collecting separately optimized PCFs to correct the MR function, the variational degrees of freedom in the relative mixing coefficients of the CSFs building the PCFs are inhibited. The constraints on the mixing coefficients lead to small off-sets in computed properties such as hyperfine structure, isotope shift and transition rates, with respect to the correct values. By (partially) deconstraining the mixing coefficients one converges to the correct limits and keeps the tremendous advantage of improved convergence rates that comes from the use of several orbital sets. Reducing ultimately each PCF to a single CSF with its own orbital basis leads to a non-orthogonal CI approach. Various perspectives of the new method are given. © 2013 IOP Publishing Ltd.
BibTeX:
@article{Verdebout2013,
  author = {Verdebout, S. and Rynkun, P. and Jönsson, P. and Gaigalas, G. and Fischer, C.F. and Godefroid, M.},
  title = {A partitioned correlation function interaction approach for describing electron correlation in atoms},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2013},
  volume = {46},
  article number = {085003},
  doi = {10.1088/0953-4075/46/8/085003}
}
Abstract: We illustrate some of the difficulties that may be encountered when computing photodissociation and radiative association cross sections from the same time-dependent approach based on wavepacket propagation. The total and partial photodissociation cross sections from the 33 vibrational levels of the b 3Σ+ state of HeH+ towards the nine other 3Σ+ and 6 3Π n = 2, 3 higher lying electronic states are calculated, using the autocorrelation method introduced by Heller (1978 J. Chem. Phys. 68 3891) and the method based on the asymptotic behaviour of wavepackets introduced by Balint-Kurti et al (1990 J. Chem. Soc. Faraday Trans. 86 1741). The corresponding radiative association cross sections are extracted from the same calculations, and the photodissociation and radiative association rate constants are determined. © 2013 IOP Publishing Ltd.
BibTeX:
@article{Vranckx2013,
  author = {Vranckx, S. and Loreau, J. and Desouter-Lecomte, M. and Vaeck, N.},
  title = {Determination of photodissociation and radiative association cross sections from the same time-dependent calculation},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2013},
  volume = {46},
  article number = {155201},
  doi = {10.1088/0953-4075/46/15/155201}
}
BibTeX:
@article{Berger2012,
  author = {Berger, G. and Gelbcke, M. and Cauët, E. and Luhmer, M. and Nève, J. and Dufrasne, F.},
  title = {Corrigendum to "Synthesis of 15N-labeled vicinal diamines through N-activated chiral aziridines: Tools for the NMR study of platinum-based anticancer compounds" [Tetrahedron Lett. 54 (2013) 545-548]},
  journal = {Tetrahedron Letters},
  year = {2012},
  doi = {10.1016/j.tetlet.2014.11.086}
}
Abstract: In a previous article we have introduced an alternative perturbation scheme to the traditional one starting from the harmonic oscillator, rigid rotator Hamiltonian, to find approximate solutions of the spectral problem for rotation-vibration molecular Hamiltonians. The convergence of our method for the methane vibrational ground state rotational energy levels was quicker than that of the traditional method, as expected, and our predictions were quantitative. In this second article, we study the convergence of the ab initio calculation of effective dipole moments for methane within the same theoretical frame. The first order of perturbation when applied to the electric dipole moment operator of a spherical top gives the expression used in previous spectroscopic studies. Higher orders of perturbation give corrections corresponding to higher centrifugal distortion contributions and are calculated accurately for the first time. Two potential energy surfaces of the literature have been used for solving the anharmonic vibrational problem by means of the vibrational mean field configuration interaction approach. Two corresponding dipole moment surfaces were calculated in this work at a high level of theory. The predicted intensities agree better with recent experimental values than their empirical fit. This suggests that our ab initio dipole moment surface and effective dipole moment operator are both highly accurate. © 2012 American Institute of Physics.
BibTeX:
@article{Cassam-Chenai2012,
  author = {Cassam-Chenaï, P. and Liévin, J.},
  title = {Ab initio calculation of the rotational spectrum of methane vibrational ground state},
  journal = {Journal of Chemical Physics},
  year = {2012},
  volume = {136},
  article number = {174309},
  doi = {10.1063/1.4705278}
}
Abstract: The Car-Parrinello-based molecular dynamics (CPMD) method was used to investigate the ion-pairing behavior between Cl - and Al 3+ ions in an aqueous AlCl 3 solution containing 63 water molecules. A series of constrained simulations was carried out at 300 K for up to 16 ps each, with the internuclear separation (r Al-Cl) between the Al 3+ ion and one of the Cl - ions held constant. The calculated potential of mean force (PMF) of the Al 3+-Cl - ion pair shows a global minimum at r Al-Cl = 2.3 Å corresponding to a contact ion pair (CIP). Two local minima assigned to solvent-separated ion pairs (SSIPs) are identified at r Al-Cl = 4.4 and 6.0 Å. The positions of the free energy minima coincide with the hydration-shell intervals of the Al 3+ cation, suggesting that the Cl - ion is inclined to reside in regions with low concentrations of water molecules, that is, between the first and second hydration shells of Al 3+ and between the second shell and the bulk. A detailed analysis of the solvent structure around the Al 3+ and Cl - ions as a function of r Al-Cl is presented. The results are compared to structural data from X-ray measurements and unconstrained CPMD simulations of single Al 3+ and Cl - ions and AlCl 3 solutions. The dipole moments of the water molecules in the first and second hydration shells of Al 3+ and in the bulk region and those of Cl - ions were calculated as a function of r Al-Cl. Major changes in the electronic structure of the system were found to result from the removal of Cl - from the first hydration shell of the Al 3+ cation. Finally, two unconstrained CPMD simulations of aqueous AlCl 3 solutions corresponding to CIP and SSIP configurations were performed (17 ps, 300 K). Only minor structural changes were observed in these systems, confirming their stability. © 2012 American Chemical Society.
BibTeX:
@article{Cauet2012,
  author = {Cauët, E. and Bogatko, S.A. and Bylaska, E.J. and Weare, J.H.},
  title = {Ion association in AlCl 3 aqueous solutions from constrained first-principles molecular dynamics},
  journal = {Inorganic Chemistry},
  year = {2012},
  volume = {51},
  pages = {10856-10869},
  doi = {10.1021/ic301346k}
}
Abstract: We present a summary of the research activities of the "Quantum Chemistry and Atomic Physics" theoretical group of the "Chimie Quantique et Photophysique" Laboratory at Université Libre de Bruxelles. We emphasize the links between the three orientations of the group: theoretical atomic spectroscopy, structure, and molecular dynamics and list the perspectives of our collaboration. © Springer-Verlag 2012.
BibTeX:
@article{Cauet2012b,
  author = {Cauët, E. and Carette, T. and Lauzin, C. and Li, J.G. and Loreau, J. and Delsaut, M. and Nazé, C. and Verdebout, S. and Vranckx, S. and Godefroid, M. and Liévin, J. and Vaeck, N.},
  title = {From atoms to biomolecules: A fruitful perspective},
  journal = {Theoretical Chemistry Accounts},
  year = {2012},
  volume = {131},
  pages = {1-17},
  doi = {10.1007/s00214-012-1254-3}
}
Abstract: Using Density Functional Theory approaches, we investigate the structure and spectroscopic signatures of sumanene, monooxosumanene and trioxosumanene, three synthesised bowl-shaped compounds. The simulated properties include geometries, charges, polarisabilities, infrared and UV/visible spectra as well as complexation energies. Refined approaches have been considered (anharmonic frequencies, state-specific solvent model, dispersion-corrected DFT...) and a valuable agreement with experimental reference values is reached for most properties. The evolution of the electronic features of sumanene upon oxidation has been rationalised. © 2011 Elsevier B.V. All rights reserved.
BibTeX:
@article{Cauet2012c,
  author = {Cauët, E. and Jacquemin, D.},
  title = {A theoretical spectroscopy investigation of oxosumanenes},
  journal = {Chemical Physics Letters},
  year = {2012},
  volume = {519-520},
  pages = {49-53},
  doi = {10.1016/j.cplett.2011.11.021}
}
Abstract: Ionization and charge migration in DNA play crucial roles in mechanisms of DNA damage caused by ionizing radiation, oxidizing agents and photo-irradiation. Therefore, an evaluation of the ionization properties of the DNA bases is central to the full interpretation and understanding of the elementary reactive processes that occur at the molecular level during the initial exposure and afterwards. Ab initio quantum mechanical (QM) methods have been successful in providing highly accurate evaluations of key parameters, such as ionization energies (IE) of DNA bases. Hence, in this study, we performed high-level QM calculations to characterize the molecular energy levels and potential energy surfaces, which shed light on ionization and charge migration between DNA bases. In particular, we examined the IEs of guanine, the most easily oxidized base, isolated and embedded in base clusters, and investigated the mechanism of charge migration over two and three stacked guanines. The IE of guanine in the human telomere sequence has also been evaluated. We report a simple molecular orbital analysis to explain how modifications in the base sequence are expected to change the efficiency of the sequence as a hole trap. Finally, the application of a hybrid approach combining quantum mechanics with molecular mechanics brings an interesting discussion as to how the native aqueous DNA environment affects the IE threshold of nucleobases.
BibTeX:
@article{Cauet2012a,
  author = {Cauët, E. and Valiev, M. and Weare, J.H. and Liévin, J.},
  title = {Quantum mechanical calculations related to ionization and charge transfer in DNA},
  journal = {Journal of Physics: Conference Series},
  year = {2012},
  volume = {373},
  article number = {012003},
  doi = {10.1088/1742-6596/373/1/012003}
}
Abstract: We investigate possible mutations in the genetic code induced by cisplatin with an approach combining molecular dynamics (MD) and hybrid quantum mechanics/molecular mechanics (QM/MM) calculations. Specifically, the impact of platination on the natural tautomeric equilibrium in guanine-cytosine (GC) base pairs is assessed to disclose the possible role played by non-canonical forms in anti-tumour activity. To obtain valuable predictions, the main interactions present in a real DNA environment, namely hydration and stacking, are simultaneously taken into account. According to our results, the Pt-DNA adduct promotes a single proton transfer reaction in GC in the DNA sequence AGGC. Such rare tautomers might play an important role in the cisplatin biological activity since they meet the stability requirements necessary to promote a permanent mutation. This journal is © the Owner Societies 2012.
BibTeX:
@article{Ceron-Carrasco2012,
  author = {Cerón-Carrasco, J.P. and Jacquemin, D. and Cauët, E.},
  title = {Cisplatin cytotoxicity: A theoretical study of induced mutations},
  journal = {Physical Chemistry Chemical Physics},
  year = {2012},
  volume = {14},
  pages = {12457-12464},
  doi = {10.1039/c2cp40515f}
}
Abstract: Spectroscopic results are presented concerning the 2CH excitation around 1.5 mm in van der Waals complexes of acetylene (C2H2) with Ar, Kr, N2, CO2, N2O and C2H 2. Many are reviewed from the literature, with some updates. Previously unpublished results are also presented, concerning the mechanism of formation of C2H2-Ar in the supersonic jet, the assignment of new spectral structures in C2H2-N2O, and the first observation of 2CH excitation in C2H2-Ne, C 2H2-H2O, C2H2-D 2O and (C2H2)n. Lifetimes of these 2CH vibrationally excited dimers are discussed. © 2012 Taylor and Francis.
BibTeX:
@article{Didriche2012,
  author = {Didriche, K. and Földes, T. and Lauzin, C. and Golebiowski, D. and Liévin, J. and Herman, M.},
  title = {Experimental 2CH excitation in acetylene-containing van der Waals complexes},
  journal = {Molecular Physics},
  year = {2012},
  volume = {110},
  pages = {2781-2796},
  doi = {10.1080/00268976.2012.705347}
}
Abstract: First-principles dynamics simulations (DFT, PBE96, and PBE0) and electron scattering calculations (FEFF9) provide near-quantitative agreement with new and existing XAFS measurements for a series of transition-metal ions interacting with their hydration shells via complex mechanisms (high spin, covalency, charge transfer, etc.). This analysis does not require either the development of empirical interparticle interaction potentials or structural models of hydration. However, it provides consistent parameter-free analysis and improved agreement with the higher-R scattering region (first- and second-shell structure, symmetry, dynamic disorder, and multiple scattering) for this comprehensive series of ions. DFT+GGA MD methods provide a high level of agreement. However, improvements are observed when exact exchange is included. Higher accuracy in the pseudopotential description of the atomic potential, including core polarization and reducing core radii, was necessary for very detailed agreement. The first-principles nature of this approach supports its application to more complex systems. © 2012 American Chemical Society.
BibTeX:
@article{Fulton2012,
  author = {Fulton, J.L. and Bylaska, E.J. and Bogatko, S. and Balasubramanian, M. and Cauët, E. and Schenter, G.K. and Weare, J.H.},
  title = {Near-quantitative agreement of model-free DFT-MD predictions with XAFS observations of the hydration structure of highly charged transition-metal ions},
  journal = {Journal of Physical Chemistry Letters},
  year = {2012},
  volume = {3},
  pages = {2588-2593},
  doi = {10.1021/jz3008497}
}
Abstract: Low-energy electrons (LEEs) play an important role in nanolithography, atmospheric chemistry, and DNA radiation damage. Previously, the cleavage of specific chemical bonds triggered by LEEs has been demonstrated in a variety of small organic molecules such as halogenated benzenes and DNA nucleobases. Here we present a strategy that allows for the first time to visualize the electron-induced dissociation of single chemical bonds within complex, but well-defined self-assembled DNA nanostructures. We employ atomic force microscopy to image and quantify LEE-induced bond dissociations within specifically designed oligonucleotide targets that are attached to DNA origami templates. In this way, we use a highly selective approach to compare the efficiency of the electron-induced dissociation of a single disulfide bond with the more complex cleavage of the DNA backbone within a Π dinucleotide sequence. This novel technique enables the fast and parallel determination of DNA strand break yields with unprecedented control over the DNA's primary and secondary structure. Thus the detailed investigation of DNA radiation damage in its most natural environment, e.g., DNA nucleosomes constituting the chromatin, now becomes feasible. © 2012 American Chemical Society.
BibTeX:
@article{Keller2012,
  author = {Keller, A. and Bald, I. and Rotaru, A. and Cauët, E. and Gothelf, K.V. and Besenbacher, F.},
  title = {Probing electron-induced bond cleavage at the single-molecule level using DNA origami templates},
  journal = {ACS Nano},
  year = {2012},
  volume = {6},
  pages = {4392-4399},
  doi = {10.1021/nn3010747}
}
Abstract: Accurate ab initio intermolecular potential energy surfaces (IPES) have been obtained for the first time for the ground electronic state of the C 2H2-Kr and C2H2-Xe van der Waals complexes. Extensive tests, including complete basis set and all-electron scalar relativistic results, support their calculation at the CCSD(T) level of theory, using small-core relativistic pseudopotentials for the rare-gas atoms and aug-cc-pVQZ basis sets extended with a set of 3s3p2d1f1g mid-bond functions. All results are corrected for the basis set superposition error. The importance of the scalar relativistic and rare-gas outer-core (n.1)d correlation effects is investigated. The calculated IPES, adjusted to analytical functions, are characterized by global minima corresponding to skew T-shaped geometries, in which the Jacobi vector positioning the rare-gas atom with respect to the center of mass of the C2H2 moiety corresponds to distances of 4.064 and 4.229Å, and angles of 65.22° and 68.67° for C 2H2-Kr and C2H2-Xe, respectively. The interaction energy of both complexes is estimated to be -151.88 (1.817 kJ mol-1) and -182.76 cm-1 (2.186 kJ mol-1), respectively. The evolution of the topology of the IPES as a function of the rare-gas atom, from He to Xe, is also discussed. © 2012 Taylor and Francis.
BibTeX:
@article{Lauzin2012,
  author = {Lauzin, C. and Cauët, E. and Demaison, J. and Herman, M. and Stoll, H. and Liévina, J.},
  title = {Accurate ground-state potential energy surfaces of the C2H 2-Kr and C2H2-Xe van der Waals complexes},
  journal = {Molecular Physics},
  year = {2012},
  volume = {110},
  pages = {2751-2760},
  doi = {10.1080/00268976.2012.713524}
}
Abstract: In the framework of the multiconfiguration Dirac-Hartree-Fock method, we investigate the transition properties of four excited states in the 2p53s configuration of neutral neon. The electron correlation effects are taken into account systematically by using the active space approach. The effect of higher-order correlation on fine structures is shown. We also study the influence of the Breit interaction and find that it reduces the oscillator strength of the 3P1o-1S0 transition by 17%. It turns out that the inclusion of the Breit interaction is essential even for such a light atomic system. Our ab initio calculated line strengths, oscillator strengths, and transition rates are compared with other theoretical values and experimental measurements. Good agreement is found except for the 3P2o-1S0 M2 transition for which discrepancies of around 15% between theories and experiments remain. In addition, the impact of hyperfine interactions on the lifetimes of the 3P0o and 3P2o metastable states is investigated for the 21Ne isotope (I=3/2). We find that hyperfine interactions reduce the lifetimes drastically. For the 3P0o state the lifetime is decreased by a factor of 630. © 2012 American Physical Society.
BibTeX:
@article{Li2012b,
  author = {Li, J. and Jönsson, P. and Godefroid, M. and Dong, C. and Gaigalas, G.},
  title = {Effects of the electron correlation and Breit and hyperfine interactions on the lifetime of the 2p53s states in neutral neon},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2012},
  volume = {86},
  article number = {052523},
  doi = {10.1103/PhysRevA.86.052523}
}
Abstract: It was recently shown that dielectronic recombination measurements can be used for accurately inferring changes in the nuclear mean-square charge radii of highly charged lithiumlike neodymium. To make use of this method to derive information about the nuclear charge distribution for other elements and isotopes, accurate electronic isotope shift parameters are required. In this work, we calculate and discuss the relativistic mass- and field-shift factors for the two 2s2S 1/2-2p2P1/2,3/2o transitions along the lithium isoelectronic sequence. Based on the multiconfiguration Dirac-Hartree-Fock method, the electron correlation and the Breit interaction are taken into account systematically. The analysis of the isotope shifts for these two transitions along the isoelectronic sequence demonstrates the importance and competition between the mass shifts and the field shifts. © 2012 American Physical Society.
BibTeX:
@article{Li2012,
  author = {Li, J. and Nazé, C. and Godefroid, M. and Fritzsche, S. and Gaigalas, G. and Indelicato, P. and Jönsson, P.},
  title = {Mass- and field-shift isotope parameters for the 2s-2p resonance doublet of lithiumlike ions},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2012},
  volume = {86},
  article number = {022518},
  doi = {10.1103/PhysRevA.86.022518}
}
Abstract: The Dirac kinetic energy (DKE) form of the normal mass shift operator (me/M ∑i=1N Ti), which is an approximation of the (1/2M ∑i=1N pi 2) operator built on the relativistic electron momenta, is widely used in relativistic atomic structure calculations. In the present paper, we illustrate the progressive breakdown of the Dirac kinetic energy form relatively to the momentum form when increasing the nuclear charge along the lithium isoelectronic sequence. Both forms are incorrect in the relativistic case but the DKE operator provides expectation values that are closer to the results obtained with the more complete relativistic recoil operator. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2012.
BibTeX:
@article{Li2012c,
  author = {Li, J.G. and Nazé, C. and Godefroid, M. and Gaigalas, G. and Jönsson, P.},
  title = {On the breakdown of the Dirac kinetic energy operator for estimating normal mass shifts},
  journal = {European Physical Journal D},
  year = {2012},
  volume = {66},
  article number = {290},
  doi = {10.1140/epjd/e2012-30328-5}
}
Abstract: Large-scale calculations have been performed using the GRASP2K package to accurately determine the lifetime of levels in 2p53s configuration of neutral neon. In particular, we calculated the hyperfine-induced transition rates from two metastable levels 3P20,0 to the ground state for odd Ne isotopes. It was found that hyperfine interactions drastically quench the lifetime of these two levels.
BibTeX:
@article{Li2012a,
  author = {Li, J.G. and Verdebout, S. and Godefroid, M.},
  title = {Ab-initio multi-configuration Dirac-Hartree-Fock calculation on the lifetimes of levels in 2p53s configuration of neutral neon},
  journal = {Journal of Physics: Conference Series},
  year = {2012},
  volume = {388},
  article number = {152007},
  doi = {10.1088/1742-6596/388/15/152007}
}
Abstract: We present a quantal study of the rotationally elastic and inelastic scattering of Ag and N 2, with the nitrogen molecule treated as a rigid rotor. The two-dimensional potential energy surface of the AgN 2 complex is obtained ab initio by means of the spin unrestricted coupled-cluster method with single, double, and perturbative triple excitations. The global minimum is found to be located at an internuclear distance of 8.13 a 0 and an angle of 127.2. The long-range part of the potential is constructed from the dynamic electric dipole polarizabilities of Ag and N 2. Elastic, excitation, and relaxation cross sections and rates are calculated for energies between 0.1 and 5000 cm -1. The momentum transfer cross sections and rates are also computed. Finally, we compare the cross sections for Ag-N 2 and Na-N 2 to explore the possibility of using silver instead of sodium in experimental tests. © 2012 American Institute of Physics.
BibTeX:
@article{Loreau2012,
  author = {Loreau, J. and Zhang, P. and Dalgarno, A.},
  title = {Scattering of nitrogen molecules by silver atoms},
  journal = {Journal of Chemical Physics},
  year = {2012},
  volume = {136},
  article number = {164305},
  doi = {10.1063/1.3703518}
}
Abstract: When the effects of the finite mass of the nucleus and the spatial nuclear charge distribution are taken into account in the Hamiltonian describing an atomic system, the isotopes of an element have different electronic energy levels. In the present work, we are investigating these mass and field effects in neutral barium, hoping to shed some light on the surprising observed deviation of isotope shifts from their expected behavior for odd isotopes in an analysis based on King-plots.
BibTeX:
@article{Naze2012,
  author = {Nazé, C. and Li, J.G. and Godefroid, M.},
  title = {Relativistic calculations on isotope shifts in barium},
  journal = {Journal of Physics: Conference Series},
  year = {2012},
  volume = {388},
  article number = {152008},
  doi = {10.1088/1742-6596/388/15/152008}
}
Abstract: When considering the work of Carl Ballhausen on vibrational spectra, it is suggested that his use of the Born-Oppenheimer approximation is capable of some refinement and extension in the light of later developments. A consideration of the potential energy surface in the context of a full Coulomb Schrödinger Hamiltonian in which translational and rotational motions are explicitly considered would seem to require a reformulation of the Born-Oppenheimer approach. The resulting potential surface for vibrational motion should be treated, allowing for the rotational motion and the nuclear permutational symmetry of the molecule. © 2011 Springer-Verlag Berlin Heidelberg.
BibTeX:
@article{Sutcliffe2012c,
  author = {Sutcliffe, B.T.},
  title = {Chemistry as a "manifestation of quantum phenomena" and the Born-Oppenheimer approximation?},
  journal = {Structure and Bonding},
  year = {2012},
  volume = {143},
  pages = {101-120},
  doi = {10.1007/430_2011_44}
}
Abstract: Transition state theory was introduced in the 1930s to account for chemical reactions. Central to this theory is the idea of a potential energy surface (PES). It was assumed that quantum mechanical computation, when it became possible, would yield such surfaces, but for the time being they would have to be constructed empirically. The approach was very successful. Nowadays, quantum mechanical ab initio electronic structure calculations are possible and from their results PESs can be constructed. Such surfaces are now widely used in the explanation of chemical reactions in place of the traditional empirical ones. It is argued here that theoretical basis of such PESs is not quite as clear as is usually assumed and that, from a quantum mechanical perspective, certain puzzles remain. © 2012 Springer-Verlag.
BibTeX:
@article{Sutcliffe2012b,
  author = {Sutcliffe, B.},
  title = {Is there an exact potential energy surface?},
  journal = {Theoretical Chemistry Accounts},
  year = {2012},
  volume = {131},
  pages = {1-11},
  doi = {10.1007/s00214-012-1215-x}
}
Abstract: The original account of the Born-Oppenheimer approximation is not mathematically secure because it is not legitimate to use perturbation theory in its development. It is necessary to use an asymptotic expansion based upon an electronic Hamiltonian defined in terms of a fiber bundle. Although with this approach it has been possible account for the traditional results for a diatomic molecule, rotational motion in the polyatomic case has not so far been accounted for. It is argued here that it is not generally possible to provide a mathematically secure account of the Born-Oppenheimer approximation for polyatomic molecules, in which rotation can be considered as a separable motion. © 2012 Wiley Periodicals, Inc. Copyright © 2012 Wiley Periodicals, Inc.
BibTeX:
@article{Sutcliffe2012a,
  author = {Sutcliffe, B.},
  title = {Some difficulties in considering rotation motion within the Born-Oppenheimer approximation for polyatomic molecules},
  journal = {International Journal of Quantum Chemistry},
  year = {2012},
  volume = {112},
  pages = {2894-2903},
  doi = {10.1002/qua.24021}
}
Abstract: This chapter starts by giving a brief account of the development of the atomic-molecular conception of chemistry. An essential backdrop to the whole discussion is the importance throughout human history of the practical chemical arts that have informed the production of the whole range of useful materials and stimulated enquiry into the theoretical aspects of chemical processes. Chemistry is concerned with the composition and properties of matter, and with the transformations of matter that can occur spontaneously or under the action of heat, radiation or other sources of energy. From the results of chemical experiments the chemist singles out a particular class of materials that have characteristic and invariant properties. Such materials are called pure substances and may be of two kinds, viz: compounds and elements. Elements may be defined as substances which have not been converted either by the action of heat, radiation, or chemical reaction with other substances, or small electrical voltages, into any simpler substance. Compounds are formed from the chemical combination of the elements, and have properties that are invariably different from the properties of the constituent elements; they are also homogeneous. This characteristic chemical notion of a pure substance is based on an ideal conception of the chemical and physical properties of matter and their changes under specified experimental conditions. © 2012 Elsevier B.V. All rights reserved.
BibTeX:
@book{Sutcliffe2012d,
  author = {Sutcliffe, B.T. and Guy Woolley, R.},
  title = {Atoms and molecules in classical chemistry and quantum mechanics},
  journal = {Philosophy of Chemistry},
  year = {2012},
  pages = {387-426},
  doi = {10.1016/B978-0-444-51675-6.50028-1}
}
Abstract: Transition state theory was introduced in 1930s to account for chemical reactions. Central to this theory is the idea of a potential energy surface (PES). It was assumed that such a surface could be constructed using eigensolutions of the Schrödinger equation for the molecular (Coulomb) Hamiltonian but at that time such calculations were not possible. Nowadays quantum mechanical ab initio electronic structure calculations are routine and from their results PESs can be constructed which are believed to approximate those assumed derivable from the eigensolutions. It is argued here that this belief is unfounded. It is suggested that the potential energy surface construction is more appropriately regarded as a legitimate and effective modification of quantum mechanics for chemical purposes. © 2012 American Institute of Physics.
BibTeX:
@article{Sutcliffe2012,
  author = {Sutcliffe, B.T. and Woolley, R.G.},
  title = {On the quantum theory of molecules},
  journal = {Journal of Chemical Physics},
  year = {2012},
  volume = {137},
  article number = {22A544},
  doi = {10.1063/1.4755287}
}
Abstract: Arguments are advanced to support the view that at present it is not possible to derive molecular structure from the full quantum mechanical Coulomb Hamiltonian associated with a given molecular formula that is customarily regarded as representing the molecule in terms of its constituent electrons and nuclei. However molecular structure may be identified provided that some additional chemically motivated assumptions that lead to the clamped nuclei Hamiltonian are added to the quantum mechanical account. © Springer Science+Business Media B.V. 2012.
BibTeX:
@book{Sutcliffe2012e,
  author = {Sutcliffe, B. and Woolley, R.G.},
  title = {The position of the clamped nuclei electronic hamiltonian in quantum mechanics},
  journal = {Handbook of Computational Chemistry},
  year = {2012},
  pages = {13-54},
  doi = {10.1007/978-94-007-0711-5_2}
}
Abstract: We investigate the photodissociation process for both hot and cold HeH + ions. Detailed comparison with experiments performed at FLASH is made possible by experimentally determining the ro-vibrational distribution of the ions under identical source conditions, and averaging the theoretical cross sections accordingly. © Published under licence by IOP Publishing Ltd.
BibTeX:
@article{Urbain2012,
  author = {Urbain, X. and Lecointre, J. and Loreau, J. and Vaeck, N.},
  title = {Photodissociation from the ground state of HeH+: Comparison with experiment},
  journal = {Journal of Physics: Conference Series},
  year = {2012},
  volume = {388},
  article number = {022107},
  doi = {10.1088/1742-6596/388/2/022107}
}
Abstract: We present some progress associated to the localised correlation function interaction (LCFI) method. In this report, the LCFI method is tested not only for total energy but also for the specific mass shift operator, the hyperfine structure parameters and the transition probabilities. These properties are computed for the three lowest electronic states of the beryllium atom. These calculations illustrate the importance of the contraction effects.
BibTeX:
@article{Verdebout2012,
  author = {Verdebout, S. and Rynkun, P. and Jönsson, P. and Gaigalast, G. and Froese Fischer, C. and Godefroid, M.},
  title = {Interaction of variational localised correlation functions for atomic properties of Be I},
  journal = {Journal of Physics: Conference Series},
  year = {2012},
  volume = {388},
  article number = {152006},
  doi = {10.1088/1742-6596/388/15/152006}
}
Abstract: (3+1) resonantly enhanced multiphoton ionization (REMPI) spectroscopy coupled to photoelectron spectroscopy (REMPI-PES) has been carried out to study the Rydberg states of HC3N in the 77,000.90,000 cm-1 region. Ab initio calculations (energies and optimized equilibrium geometries) have been performed for the first time for the low-lying X̃2Π, Ã 2Σ+ and B̃2Π states of the cation HC3N+ in order to help the analysis. Thanks to the combination of the three-photon REMPI spectra, one-photon spectrum and photoelectron spectra, unambiguous assignments of the Rydberg series and their vibrationally excited members are proposed. The electronic Rydberg structure of cyanoacetylene is very similar to that of C2H2 and HCN (almost identical quantum defects), fully supporting the present analysis. New three-photon allowed Rydberg series are identified belonging to ns and nd series. The three-photon vibrational band assignments, confirmed by the photoelectrons spectra, reveal excitation of only one or two quanta of the v1 (C≅N) mode. Apparent discrepancies between the three-photon REMPI spectrum and the one-photon absorption spectrum are removed via a minor re-assignment of the absorption spectrum previously analysed by Connors et al. J. Chem. Phys. 60(12), 5011 (1974). Finally the observed analogy with C 2H2 and HCN can be rationalized by a partial relocalization of the 2π electrons upon excitation to Rydberg states converging to the X̃2Π state of HC3N+, as predicted by the present ab initio calculations on the cation core. © 2012 Taylor and Francis.
BibTeX:
@article{VieiraMendes2012,
  author = {Vieira Mendes, L.A. and Boyé-Péronne, S. and Jacovella, U. and Liévin, J. and Gauyacq, D.},
  title = {Rydberg states of cyanoacetylene investigated by (3+1) REMPI spectroscopy in the 77,000.90,000 cm-1 energy range},
  journal = {Molecular Physics},
  year = {2012},
  volume = {110},
  pages = {2829-2842},
  doi = {10.1080/00268976.2012.706327}
}
Abstract: Although it is thought to play an important role in the chemistry of some extra-terrestrial environments, the HeH+ cation has not been detected in space so far. We suggest it could be observed in its triplets rather than singlet states and we study the formation by radiative stabiliation and the destruction by photodissociation of the two lowest states of this symmetry. © Published under licence by IOP Publishing Ltd.
BibTeX:
@article{Vranckx2012a,
  author = {Vranckx, S. and Loreau, J. and Desouter-Lecomte, M. and Vaeck, N.},
  title = {Radiative stabilization and photodissociation of HeH+ in its two lowest 3Σ+ states},
  journal = {Journal of Physics: Conference Series},
  year = {2012},
  volume = {388},
  article number = {022109},
  doi = {10.1088/1742-6596/388/2/022109}
}
Abstract: We implement a local control strategy based on the use of Moller operators and use it to control the photodissociation of diatomic molecules in the presence of nonadiabatic interactions.
BibTeX:
@article{Vranckx2012,
  author = {Vranckx, S. and Meier, C. and Bomble, L. and Chenel, A. and Desouter-Lecomte, M. and Vaeck, N.},
  title = {Local control of nonadiabatic photodissociation dynamics using Moller operators},
  journal = {Journal of Physics: Conference Series},
  year = {2012},
  volume = {388},
  article number = {112009},
  doi = {10.1088/1742-6596/388/11/112009}
}
Abstract: The hyperfine structure constants for the ground 4s24p 2P°3/2 and lowest excited states 4s25s 2S1/2 of 71Ga are calculated using the GRASP2K package based on the multi-configuration Dirac-Hartree-Fock method. Furthermore, the magnetic dipole (μ) and the electric quadrupole (Q) moments of the Ga isotopes from 67Ga to 81Ga are derived.
BibTeX:
@article{Wang2012,
  author = {Wang, Q.M. and Li, J.G. and Fritzsche, S. and Godefroid, M. and Chang, Z.W. and Dong, C.Z.},
  title = {Theoretical study of hyperfine structure constants of Ga isotopes},
  journal = {Journal of Physics: Conference Series},
  year = {2012},
  volume = {388},
  article number = {152009},
  doi = {10.1088/1742-6596/388/15/152009}
}
Abstract: The radiative properties of the W 5 + ion are investigated using two independent theoretical approaches, i.e. the HartreeFock method with relativistic corrections of Cowan and the multiconfiguration DiracHartreeFock method as implemented in the grasp2k package. The corevalence correlations are studied in detail comparing models where a core-polarization model potential plus a correction to the dipole operator are considered (HFR + CPOL) on the one hand, and core-excited configurations are explicitly included in the configuration-interaction expansion of the atomic state function on the other hand. In general, a good agreement is found between the two theoretical methods. Core-polarization effects are remarkably strong lengthening the lifetimes up to 15%35% and even by a factor of 2 for the 5f levels. The lifetimes of the two 5f levels are found to be model dependent and particularly sensitive to core-penetration effects; precise measurements are clearly needed here. © 2012 IOP Publishing Ltd.
BibTeX:
@article{Yoca2012,
  author = {Yoca, S.E. and Palmeri, P. and Quinet, P. and Jumet, G. and Biémont, E.},
  title = {Radiative properties and core-polarization effects in the W 5+ ion},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2012},
  volume = {45},
  article number = {035002},
  doi = {10.1088/0953-4075/45/3/035002}
}
Abstract: Aqua/hydroxo mononuclear Al3+ species coordinated by F - in aqueous solution are investigated using density functional theory (DFT B3LYP/6-311++G(d,p)) and the polarized continuum model (PCM). Optimized gas-phase geometries have been obtained for the species AlF(OH) n(H2O)m(2-n)+ in which n = 0, 1, 2, or 3 while (n + m) = 3, 4, or 5. Analysis of the Al-F, Al-O, and O-H bond lengths and the Al, F, O, and H natural charges of these complexes reveals clear trends that suggest increased acidity with decreasing coordination number (CN) and decreased water stability with increased hydrolysis. These observations are supported by the calculation and analysis of the dehydration and hydrolysis reaction Gibbs free energies δGaqueous dehydration and δGaqueous hydrolysis of the AlF(OH)n(H2O)m(2-n) + complexes, which clearly show a strong correlation between increased hydrolysis and a preference to coordinate fewer water molecules. The combination of the appropriate δGaqueous dehydration and δGaqueous hydrolysis values generate the aqueous Gibbs free energies relative to AlF(H2O)52+ and demonstrate the clear transition from a 6 to 5 to 4 coordinate species as a function of ligand hydrolysis. Calculation of the equilibrium mole fraction of each species as a function of pH shows that this system is largely dominated by the AlF(OH) 1(H2O)41+ and AlF(OH) 31- species. A comparison of structural and electronic data with the aqueous Al3+ complexes shows a remarkable similarity when plotted against the number negative ligands (F- or OH -), suggesting that the F- anion coordinates the Al 3+ cation in a similar way to the remaining OH- anions. The comparison of the calculated equilibrium mole fractions of each species displays important changes in the composition of our model system upon Al 3+ coordination by F- in the direction of increased acidity of these complexes. Our predicted decreased stability of the Al-water bond is in complete agreement with experimental NMR observations of an increased water exchange rate upon F- coordination of aqueous aluminum complexes. Our prediction of stable hydroxide ternary complexes is not in agreement with recent NMR data, which indicate that these complexes do not readily form. An explanation for this may lie in the increased lability of these complexes, which may lead to difficulties in NMR detection. © 2011 American Chemical Society.
BibTeX:
@article{Bogatko2011,
  author = {Bogatko, S. and Cauët, E. and Geerlings, P.},
  title = {Influence of F- coordination on Al3+ hydrolysis reactions from density functional theory calculations},
  journal = {Journal of Physical Chemistry C},
  year = {2011},
  volume = {115},
  pages = {6910-6921},
  doi = {10.1021/jp112076r}
}
Abstract: We present highly correlated multi-configuration Hartree-Fock (MCHF) calculations of the hyperfine structure of the 3p 5 2P o J levels of 33S - and 35, 37Cl. We obtain good agreement with observation. The hyperfine structure of the neutral sulphur 33S 3p 4 3P J lowest multiplet that has never been measured to the knowledge of the authors is also estimated theoretically. We discuss some interesting observations made on the description of the atomic core in MCHF theory. © 2011 IOP Publishing Ltd.
BibTeX:
@article{Carette2011,
  author = {Carette, T. and Godefroid, M.R.},
  title = {Ab initio calculations of the 33S 3p 4 3P J and 33S -/ 37, 35Cl 3p 5 2P o J hyperfine structures},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2011},
  volume = {44},
  article number = {105001},
  doi = {10.1088/0953-4075/44/10/105001}
}
Abstract: This work is an ab initio study of the 2p34S3/2o, and 2D3/2,5/2o states of C- and 2p23P0,1,2, 1D2, and 1S0 states of neutral carbon. We use the multiconfiguration Hartree-Fock approach, focusing on the accuracy of the wave function itself. We obtain all C - detachment thresholds, including correlation effects to about 0.5%. Isotope shifts and hyperfine structures are calculated. The achieved accuracy of the latter is of the order of 0.1 MHz. Intraconfiguration transition probabilities are also estimated. © 2011 American Physical Society.
BibTeX:
@article{Carette2011a,
  author = {Carette, T. and Godefroid, M.R.},
  title = {Theoretical study of the C- 4S3/2o and 2D3/2,5/2o bound states and C ground configuration: Fine and hyperfine structures, isotope shifts, and transition probabilities},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2011},
  volume = {83},
  article number = {062505},
  doi = {10.1103/PhysRevA.83.062505}
}
Abstract: Ab initio quantum mechanical methods provide microscopic insights into DNA characteristics and are, today, essential to the full interpretation and understanding of results obtained by experimental techniques. In this chapter we summarize the contributions of modern quantum chemicalcalculations to the determination of the electronic properties of DNA bases, isolated or embedded in base clusters. In particular, the calculations discussed concern the characterization of the molecular energy levels and potential energy surfaces, which shed light on ionization and charge migration along DNA molecules. We mainly consider the estimation of key parameters, such as ionization potentials (IPs) of DNA bases, which govern the charge injection into DNA. The effects of the stacking and H-bonding DNA base interactions and the solvation of DNA on these quantities are described. We also discuss the mechanisms of charge migration over stacked DNA bases. These aspects are illustrated by a survey of the literature and by our own selected recent results. © 2012 by Nova Science Publishers, Inc. All rights reserved.
BibTeX:
@book{Cauet2011a,
  author = {Cauët, E.},
  title = {Quantum mechanical methods related to ionization of nucleic acid bases},
  journal = {DNA Microarrays, Synthesis and Synthetic DNA},
  year = {2011},
  pages = {255-284}
}
Abstract: The hypothetical protection of genes from oxidative damage provided by the G-rich telomeric overhangs located at the end of chromosomes, which consist, in humans, of single strands of TTAGGG sequence repeats, is investigated here. First principle Møller-Plesset perturbation theory calculations reveal that the TTAGGG human telomere sequence is particularly prone to oxidation and can act as a profound hole trap as deep as a sequence of five consecutive guanines. In addition, we show that the sequence dependence is very important and that modifications in the human telomeric sequence can induce crucial changes in the electronic structure of the sequence, with concomitant increase of the ionization energy. These theoretical results provide, for the first time, quantitative data indicating a high and unique efficiency of the human telomeric sequence as a trap in long-range hole migration which will aid in the design of subsequent experiments. © 2011 Taylor & Francis Group, LLC.
BibTeX:
@article{Cauet2011,
  author = {Cauët, E.},
  title = {Unique hole-trapping property of the human telomere sequence},
  journal = {Journal of Biomolecular Structure and Dynamics},
  year = {2011},
  volume = {29},
  pages = {557-561},
  doi = {10.1080/07391102.2011.10507405}
}
Abstract: Within the lowest-order relativistic approximation (∼v 2/c2) and to first order in me/M, the tensorial form of the relativistic corrections of the nuclear recoil Hamiltonian is derived, opening interesting perspectives for calculating isotope shifts in the multiconfiguration Dirac-Hartree-Fock framework. Their calculation is illustrated for selected Li-, B- and C-like ions. This work underlines the fact that the relativistic corrections to the nuclear recoil are definitively necessary for obtaining reliable isotope shift values. © 2011 IOP Publishing Ltd.
BibTeX:
@article{Gaidamauskas2011,
  author = {Gaidamauskas, E. and Nazé, C. and Rynkun, P. and Gaigalas, G. and Jönsson, P. and Godefroid, M.},
  title = {Tensorial form and matrix elements of the relativistic nuclear recoil operator},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2011},
  volume = {44},
  article number = {175003},
  doi = {10.1088/0953-4075/44/17/175003}
}
Abstract: The equilibrium structure of acetylene (also named ethyne) has been reinvestigated to resolve the small discrepancies noted between different determinations. The size of the system as well as the large amount of available experimental data provides the quite unique opportunity to check the magnitude and relevance of various contributions to equilibrium structure as well as to verify the accuracy of experimental results. With respect to pure theoretical investigation, quantum-chemical calculations at the coupled-cluster level have been employed together with extrapolation to the basis set limit, consideration of higher excitations in the cluster operator, inclusion of core correlation effects as well as relativistic and diagonal Born-Oppenheimer corrections. In particular, it is found that the extrapolation to the complete basis set limit, the inclusion of higher excitations in the electronic-correlation treatment and the relativistic corrections are of the same order of magnitude. It also appears that a basis set as large as a core-valence quintuple-zeta set is required for accurately accounting for the inner-shell correlation contribution. From a pure experimental point of view, the equilibrium structure has been determined using very accurate rotational constants recently obtained by a global analysis (that is to say that all non-negligible interactions are explicitely included in the Hamiltonian matrix) of rovibrational spectra. Finally, a semi-experimental equilibrium structure (where the equilibrium rotational constants are obtained from the experimental ground state rotational constants and computed rovibrational corrections) has been obtained from the available experimental ground-state rotational constants for ten isotopic species corrected for computed vibrational corrections. Such a determination led to the revision of the ground-state rotational constants of two isotopologues, thus showing that structural determination is a good method to identify errors in experimental rotational constants. The three structures are found in a very good agreement, and our recommended values are rCC 120.2958(7) pm and rCH 106.164(1) pm. © 2011 American Institute of Physics.
BibTeX:
@article{Lievin2011,
  author = {Liévin, J. and Demaison, J. and Herman, M. and Fayt, A. and Puzzarini, C.},
  title = {Comparison of the experimental, semi-experimental and ab initio equilibrium structures of acetylene: Influence of relativisitic effects and of the diagonal Born-Oppenheimer corrections},
  journal = {Journal of Chemical Physics},
  year = {2011},
  volume = {134},
  article number = {064119},
  doi = {10.1063/1.3553203}
}
Abstract: We investigate the dynamics of the photodissociation of the helium hydride ion HeH+ by XUV radiation with the aim to establish a detailed comparison with a recent experimental work carried out at the FLASH free electron laser using both vibrationally hot and cold ions. We determine the corresponding rovibrational distributions using a dissociative charge transfer setup and the same source conditions as in the FLASH experiment. Using a nonadiabatic time-dependent wave-packet method, we calculate the partial photodissociation cross sections for the n=1-3 coupled electronic states of HeH+. We find good agreement with the experiment for the cross section into the He + H+ dissociative channel. On the other hand, we show that the experimental observation of the importance of the electronic states with n>3 cannot be well explained theoretically, especially for cold (v=0) ions. We find a good agreement with the experiment on the relative contribution of the Σ and Π states to the cross section for the He + + H channel, but only a qualitative one for the He + H+ channel. We discuss the factors that could explain the remaining discrepancies between theory and experiment. © 2011 American Physical Society.
BibTeX:
@article{Loreau2011b,
  author = {Loreau, J. and Lecointre, J. and Urbain, X. and Vaeck, N.},
  title = {Rovibrational analysis of the XUV photodissociation of HeH+ ions},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2011},
  volume = {84},
  article number = {053412},
  doi = {10.1103/PhysRevA.84.053412}
}
Abstract: We present a theoretical study of the isotope effect arising from the replacement of H by T in the charge-transfer collision H(n=2) + He +(1s) at low energy. Using a quasimolecular approach and a time-dependent wave-packet method, we compute the cross sections for the reaction including the effects of the nonadiabatic radial and rotational couplings. For H(2s) + He+(1s) collisions, we find a strong isotope effect at energies below 1 eV/amu for both singlet and triplet states. We find a much smaller isotopic dependence of the cross section for H(2p) + He +(1s) collisions in triplet states, and no isotope effect in singlet states. We explain the isotope effect on the basis of the potential energy curves and the nonadiabatic couplings, and we evaluate the importance of the isotope effect on the charge-transfer rate coefficients. © 2011 American Physical Society.
BibTeX:
@article{Loreau2011a,
  author = {Loreau, J. and Ryabchenko, S. and Dalgarno, A. and Vaeck, N.},
  title = {Isotope effect in charge-transfer collisions of H with He+},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2011},
  volume = {84},
  article number = {052720},
  doi = {10.1103/PhysRevA.84.052720}
}
Abstract: A quantal study of the rotational excitation of nitrogen molecules by sodium atoms is carried out. We present the two-dimensional potential energy surface of the NaN2 complex, with the N2 molecule treated as a rigid rotor. The interaction potential is computed using the spin unrestricted coupled-cluster method with single, double, and perturbative triple excitations (UCCSD(T)). The long-range part of the potential is constructed from the dynamic electric dipole polarizabilities of Na and N2. The total, differential, and momentum transfer cross sections for rotationally elastic and inelastic transitions are calculated using the close-coupling approach for energies between 5 cm-1 and 1500 cm-1. The collisional and momentum transfer rate coefficients are calculated for temperatures between 100 K and 300 K, corresponding to the conditions under which Na-N2 collisions occur in the mesosphere. © 2011 American Institute of Physics.
BibTeX:
@article{Loreau2011,
  author = {Loreau, J. and Zhang, P. and Dalgarno, A.},
  title = {Elastic scattering and rotational excitation of nitrogen molecules by sodium atoms},
  journal = {Journal of Chemical Physics},
  year = {2011},
  volume = {135},
  article number = {174301},
  doi = {10.1063/1.3653983}
}
Abstract: Electron holes are known to migrate along the DNA or RNA duplexes and to localize preferentially on successive guanines. The stationary point conformations of Gua pairs that can trap or let pass these holes have been characterized by quantum chemistry calculations. Here we show their recurrent occurrence in DNA and RNA X-ray structures, often in quadruplex conformations or in interaction with proteins, ligands or metal ions. These findings give support to the biological, possibly regulatory, roles of charge migration in cell functioning. © 2011 Taylor & Francis Group, LLC.
BibTeX:
@article{Rooman2011,
  author = {Rooman, M. and Cauët, E. and Liévin, J. and Wintjens, R.},
  title = {Conformations consistent with charge migration observed in dna and rna x-ray structures},
  journal = {Journal of Biomolecular Structure and Dynamics},
  year = {2011},
  volume = {28},
  pages = {949-954},
  doi = {10.1080/073911011010524985}
}
Abstract: The spectroscopy of the ZrF radical, produced by a laser ablation-molecular beam experimental setup, has been investigated for the first time using a two-color two-photon (1 + 1′) REMPI scheme and time-of-flight (TOF) mass spectrometry detection. The region of intense bands 400-470 nm has been studied, based upon the first spectroscopic observations of the isovalent ZrCl radical by Carroll and Daly.(1)The overall spectrum observed is complex. However, simultaneous and individual ion detection of the five naturally occurring isotopologues of ZrF has provided a crucial means of identifying band origins and characterization via the isotopic shift, δ iso, of the numerous vibronic transitions recorded. Hence, five (0-0) transitions, of which only two were free of overlap with other transitions, have been identified. The most intense (0-0) transition at 23113 cm -1 presented an unambiguously characteristic RQP rotational structure. From rotational contour simulations of the observed spectra, the nature of the ground electronic state is found to be unambiguously of 2Δ symmetry, leading to the assignment of this band as (0-0) 2Δ ← X 2Δ at 23113 cm -1. A set of transitions (1-0) 2Δ ← X 2Δ at 22105 cm -1 and (2-0) 2 ← X 2Δ at 22944 cm -1 involving the X 2Δ state has also been identified and analyzed. Furthermore, a second series of transitions with lesser intensity has also been related to the long-lived metastable 4Σ - state: (3-0) 4Π -1/2 ← 4Σ - at 21801 cm -1, (2-0) 4Π -1/2 ← 4Σ - at 21285 cm -1 and (2-0) 4Σ - ← 4Σ - at 23568 cm -1. These spectroscopic assignments are supported by MRCI ab initio calculations, performed using the MOLPRO quantum chemistry package, and show that the low-lying excited states of the ZrF radical are the 4Σ - and 4 states lying at 2383 and 4179 cm -1 respectively above the ground X 2Δ state. The difference in the nature of ground state and ordering of the first electronic states with TiF (X 4)(2-4)and ZrCl,(5)respectively, is examined in terms of the ligand field theory (LFT)(7)applied to diatomic molecules. These results give a precise description of the electronic structure of the low lying electronic states of the ZrF transition metal radical. © 2011 American Chemical Society.
BibTeX:
@article{Soorkia2011,
  author = {Soorkia, S. and Shafizadeh, N. and Liévin, J. and Gaveau, M.-A. and Pothier, C. and Mestdagh, J.-M. and Soep, B. and Field, R.W.},
  title = {Determination of the ground electronic state in transition metal halides: ZrF},
  journal = {Journal of Physical Chemistry A},
  year = {2011},
  volume = {115},
  pages = {9620-9632},
  doi = {10.1021/jp2004997}
}
Abstract: It is argued that whether the use of the Born--Oppenheimer approximation is thought to require consideration of the potential energy surface in the context of a full Coulomb Schrödinger Hamiltonian in which translational and rotational motions are explicitly considered, and then it is inconsistent to treat that surface without allowing for the rotational motion of the molecule. Some of the implications of this upon the calculation of partition functions are considered. © 2011 Springer-Verlag.
BibTeX:
@article{Sutcliffe2011,
  author = {Sutcliffe, B.T.},
  title = {An analysis of the role of the Born--Oppenheimer approximation in calculating rotational--vibrational interactions in molecules},
  journal = {Theoretical Chemistry Accounts},
  year = {2011},
  volume = {130},
  pages = {187-195},
  doi = {10.1007/s00214-011-0953-5}
}
BibTeX:
@article{Sutcliffe2011a,
  author = {Sutcliffe, B.T. and Woolley, R.G.},
  title = {A comment on "Editorial 37"},
  journal = {Foundations of Chemistry},
  year = {2011},
  volume = {13},
  pages = {93-95},
  doi = {10.1007/s10698-011-9110-4}
}
Abstract: A single band belonging to the Ã′2Δ- X̃2Σ+ band system has been rotationally analyzed for each of the two isotopologues, BaOH and BaOD, using high-resolution V-type optical-optical double resonance spectroscopy. BaOH and BaOD molecules were synthesized in a Broida-type oven. High-resolution spectra were recorded by monitoring the dip in fluorescence of the B2Σ+- X2Σ+ transition excited by a single-mode ring dye laser (pump laser), whilst a single-mode Ti:Sapphire laser scanned the corresponding Ã′2Δ-X̃2 Σ+ transition. The observed spectra resemble a typical 2Π-2Σ transition, believed to emanate from single or triple quanta of the bending vibration in the à ′2Δ state. Measured rotational lines have been assigned and rotational and fine structure parameters determined through a combined least-squares fit with the millimeter-wave pure rotational data of the X 2Σ+ state. Previous analyses of the Ã2Π-X̃2Σ+ transitions of BaOH and BaOD yielded significantly different spin-orbit coupling constants, which were attributed to possible global and local perturbations arising from vibrationally-excited bands of the A′2Δ state. Although the newly observed A′2Δ state bands have not been conclusively assigned a specific spin state, the derived Ω-doubling constants show significant 2Π1/2 character, further indicating strong interactions between the A2Π and A ′2Δ states of BaOH. To validate these conclusions, ab initio calculations have been carried out to further understand the nature of the BaOH excited states. The D̃′2Σ+, D̃2Σ+, C̃2Π, B̃2Σ+, Ã2Π, Ã′2Δ and X̃2Σ+ states have been characterized by means of multireference configuration interaction calculations using the MOLPRO software. Calculated vertical term energies show relatively good agreement with existing optical data. © 2011 Elsevier Inc. All rights reserved.
BibTeX:
@article{Tandy2011,
  author = {Tandy, J.D. and Wang, J.-G. and Liévin, J. and Bernath, P.F.},
  title = {Investigating the electronic states of BaOH by V-type double resonance spectroscopy and ab initio calculations: Further evidence of perturbation from the Ã′2Δ state},
  journal = {Journal of Molecular Spectroscopy},
  year = {2011},
  volume = {270},
  pages = {44-50},
  doi = {10.1016/j.jms.2011.08.009}
}
Abstract: Amino-acid enantiomeric excesses (ee's) have been detected in different types of carbonaceous chondrites, all in favor of the L enantiomer. In this article, we discuss possible deterministic causes to the presence of these amino-acid ee's in meteorites and evaluate in particular enantioselective photolysis by circularly polarized light (CPL). The electronic circular dichroism spectra of a set of amino- and hydroxy-acids, all detected in chondritic matter but some with ee's and others without ee's, were calculated and compared. The spectra were calculated for the most stable conformation(s) of the considered molecules using quantum mechanical methods (density functional theory). Our results suggest that CPL photolysis in the gas phase was perhaps not at the origin of the presence of ee's in meteorites and that the search for another, but still unknown, deterministic cause must be seriously undertaken. © 2011 Wiley-Liss, Inc.
BibTeX:
@article{Vandenbussche2011,
  author = {Vandenbussche, S. and Reisse, J. and Bartik, K. and Lievin, J.},
  title = {The search for a deterministic origin for the presence of nonracemic amino-acids in meteorites: A computational approach},
  journal = {Chirality},
  year = {2011},
  volume = {23},
  pages = {367-373},
  doi = {10.1002/chir.20933}
}
Abstract: A new atsp2K module is presented for evaluating the electron density function of any multiconfiguration Hartree-Fock or configuration interaction wave function in the non-relativistic or relativistic Breit-Pauli approximation. It is first stressed that the density function is not a priori spherically symmetric in the general open shell case. Ways of building it as a spherical symmetric function are discussed, from which the radial electron density function emerges. This function is written in second quantized coupled tensorial form for exploring the atomic spherical symmetry. The calculation of its expectation value is performed using the angular momentum theory in orbital, spin, and quasispin spaces, adopting a generalized graphical technique. The natural orbitals are evaluated from the diagonalization of the density matrix. Program summary: Program title: DENSITY. Catalogue identifier: AEFR_v1_0. Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEFR_v1_0.html. Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland. Licensing provisions: Standard CPC license, http://cpc.cs.qub.ac.uk/licence/licence.html. No. of lines in distributed program, including test data, etc.: 6603. No. of bytes in distributed program, including test data, etc.: 169 881. Distribution format: tar.gz. Programming language: FORTRAN 90. Computer: HP XC Cluster Platform 4000. Operating system: HP XC System Software 3.2.1, which is a Linux distribution compatible with Red Hat Enterprise Advanced Server. Word size: 32 bits. Classification: 2.1, 2.9, 4.1. Subprograms used:A table is presented. Nature of problem: This program determines the atomic electronic density in the MCHF (LS) or Breit-Pauli (LS J) approximation. It also evaluates the natural orbitals by diagonalizing the density matrix. Solution method: Building the density operator using second quantization - spherical symmetry averaging - evaluating the matrix elements of the one-body excitation operators in the configuration state function (CSF) space using the angular momentum theory in orbital, spin, and quasispin spaces. Restrictions: Original restrictions from ATSP2K package, i.e. all orbitals within a wave function expansion are assumed to be orthonormal. Configuration states are restricted to at most eight subshells in addition to the closed shells common to all configuration states. The maximum size of the working arrays, related to the number of CSFs and active orbitals, is limited by the available memory and disk space. Unusual features: The programming style is essentially F77 with extensions for the POINTER data type and associated memory allocation. These have been available on workstations for more than a decade, but their implementations are compiler dependent. The present code has been installed and tested extensively using the Portland Group, pgf90, compiler. Running time: The calculation of the electron density for an n = 9 complete active space (CAS) MCHF wave function (271 733 CSFs - 45 orbitals) takes around 9 minutes on one AMD Opteron dual-core at 2.4 GHz CPU. References: [1]C. Froese Fischer, G. Tachiev, G. Gaigalas, M.R. Godefroid, An MCHF atomic-structure package for large-scale calculation, Comput. Phys. Commun. 176 (2007) 559-579. © 2009 Elsevier B.V. All rights reserved.
BibTeX:
@article{Borgoo2010,
  author = {Borgoo, A. and Scharf, O. and Gaigalas, G. and Godefroid, M.},
  title = {Multiconfiguration electron density function for the ATSP2K-package},
  journal = {Computer Physics Communications},
  year = {2010},
  volume = {181},
  pages = {426-439},
  doi = {10.1016/j.cpc.2009.10.014}
}
Abstract: The sulfur electron affinities eA(S) are measured by photodetachment microscopy for the two isotopes S32 and S34 (16752.9753(41) and 16752.9776(85) cm-1, respectively). The isotope shift in the electron affinity is found to be more probably positive, eA(S34)-eA(S32) =+0.0023(70) cm -1, but the uncertainty allows for the possibility that it may be either "normal" [eA(S34) eA(S32)] or "anomalous" [eA(S34) <eA(S32)]. The isotope shift is estimated theoretically using elaborate correlation models, monitoring the electron affinity and the mass polarization term expectation value. The theoretical analysis predicts a very large specific mass shift (SMS) that counterbalances the normal mass shift (NMS) and produces an anomalous isotope shift eA(S34)-eA(S32) =-0.0053(24) cm-1, field shift corrections included. The total isotope shift can always be written as the sum of the NMS (here +0.0169 cm-1) and a residual isotope shift (RIS). Since the NMS has nearly no uncertainty, the comparison between experimental and theoretical RIS is more fair. With respective values of -0.0146(70) cm-1 and -0.0222(24) cm-1, these residual isotope shifts are found to agree within the estimated uncertainties. © 2010 The American Physical Society.
BibTeX:
@article{Carette2010,
  author = {Carette, T. and Drag, C. and Scharf, O. and Blondel, C. and Delsart, C. and Froese Fischer, C. and Godefroid, M.},
  title = {Isotope shift in the sulfur electron affinity: Observation and theory},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2010},
  volume = {81},
  article number = {042522},
  doi = {10.1103/PhysRevA.81.042522}
}
Abstract: The hyperfine constants of the levels 2p 2 (3P)3s 4P J, 2p 2 (3P)3p 4P o J and 2p 2 (3P)3p 4D o J, deduced by Jennerich et al. [Eur. Phys. J. D 40, 81 (2006)] from the observed hyperfine structures of the transitions 2p 2 (3P)3s 4P J→ 2p2 (3P)3p 4P o J and 2p 2 (3P)3s 4P J→ 2p 2 ( 3P)3p 4D o J recorded by saturation spectroscopy in the near-infrared, strongly disagree with the ab initio values of Jönsson et al. [J. Phys. B: At. Mol. Opt. Phys. 43, 115006 (2010)]. We propose a new interpretation of the recorded weak spectral lines. If the latter are indeed reinterpreted as crossover signals, a new set of experimental hyperfine constants is deduced, in very good agreement with the ab initio predictions. © 2010 EDP Sciences, SIF, Springer-Verlag Berlin Heidelberg.
BibTeX:
@article{Carette2010a,
  author = {Carette, T. and Nemouchi, M. and Jönsson, P. and Godefroid, M.},
  title = {Saturation spectra of low lying states of Nitrogen: Reconciling experiment with theory},
  journal = {European Physical Journal D},
  year = {2010},
  volume = {60},
  pages = {231-242},
  doi = {10.1140/epjd/e2010-00241-2}
}
Abstract: The unprotonated and protonated monoreduced forms of the polyazaaromatic Ru(II) coordination complexes [Ru(tap)3]2+ and [Ru(tap)2(phen)]2+ (tap = 1,4,5,8-tetraazaphenanthrene; phen = 1,10-phenanthroline), that is, [Ru(tap)3]•+, [Ru(tap)2(phen)]•+, [Ru(tap)2(tap-H)] •2+, and [Ru(tap)(tap-H)(phen)]•2+, were studied by Density Functional Theory (DFT). The electron spin density of these radical cations, the isotropic Fermi-contact, and the anisotropic dipolar contributions to the hyperfine coupling constants of the H nuclei were calculated in vacuo and using a continuum model for water solvation. For [Ru(tap)2(phen)] •+, as well as for its protonated form, the DFT results show that the unpaired electron is not localized on the phen ligand. For both [Ru(tap)3]•+ and [Ru(tap)2(phen)] •+, they reveal high electron spin density in the vicinity of tap H-2 and tap H-7 (the H atoms in the ortho position of the tap non-chelating N atoms). These results are in full agreement with recent steady-state 1H photo-Chemically Induced Dynamic Nuclear Polarization (photo-CIDNP) measurements. The DFT calculations performed for the protonated species also predict major 1H photo-CIDNP enhancements at these positions. Interestingly, they indicate significantly different polarization for tap H-9,10, suggesting that the occurrence of a photoinduced electron transfer with protonation of the reduced species might be detected by high-precision photo-CIDNP experiments. © 2010 American Chemical Society.
BibTeX:
@article{Cauet2010,
  author = {Cauët, E. and Bogatko, S. and Mugeniwabagara, E. and Fusaro, L. and Kirsch-De Mesmaeker, A. and Luhmer, M. and Vaeck, N.},
  title = {Density functional theory interpretation of the 1H photo-chemically induced dynamic nuclear polarization enhancements characterizing photoreduced polyazaaromatic Ru(II) coordination complexes},
  journal = {Inorganic Chemistry},
  year = {2010},
  volume = {49},
  pages = {7826-7831},
  doi = {10.1021/ic100636j}
}
Abstract: Results of ab initio molecular dynamics (AIMD) simulations (density functional theory+PBE96) of the dynamics of waters in the hydration shells surrounding the Zn2+ ion (T≈300 K, ρ ≈1 gm/ cm3) are compared to simulations using a combined quantum and classical molecular dynamics [AIMD/molecular mechanical (MM)] approach. Both classes of simulations were performed with 64 solvating water molecules (∼15 ps) and used the same methods in the electronic structure calculation (plane-wave basis set, time steps, effective mass, etc.). In the AIMD/MM calculation, only six waters of hydration were included in the quantum mechanical (QM) region. The remaining 58 waters were treated with a published flexible water-water interaction potential. No reparametrization of the water-water potential was attempted. Additional AIMD/MM simulations were performed with 256 water molecules. The hydration structures predicted from the AIMD and AIMD/MM simulations are found to agree in detail with each other and with the structural results from x-ray data despite the very limited QM region in the AIMD/MM simulation. To further evaluate the agreement of these parameter-free simulations, predicted extended x-ray absorption fine structure (EXAFS) spectra were compared directly to the recently obtained EXAFS data and they agree in remarkable detail with the experimental observations. The first hydration shell contains six water molecules in a highly symmetric octahedral structure is (maximally located at 2.13-2.15 Å versus 2.072 Å EXAFS experiment). The widths of the peak of the simulated EXAFS spectra agree well with the data (8.4 Å2 versus 8.9 Å2 in experiment). Analysis of the H-bond structure of the hydration region shows that the second hydration shell is trigonally bound to the first shell water with a high degree of agreement between the AIMD and AIMD/MM calculations. Beyond the second shell, the bonding pattern returns to the tetrahedral structure of bulk water. The AIMD/MM results emphasize the importance of a quantum description of the first hydration shell to correctly describe the hydration region. In these calculations the full d10 electronic structure of the valence shell of the Zn2+ ion is retained. The simulations show substantial and complex charge relocation on both the Zn 2+ ion and the first hydration shell. The dipole moment of the waters in the first hydration shell is 3.4 D (3.3 D AIMD/MM) versus 2.73 D bulk. Little polarization is found for the waters in the second hydration shell (2.8 D). No exchanges were seen between the first and the second hydrations shells; however, many water transfers between the second hydration shell and the bulk were observed. For 64 waters, the AIMD and AIMD/MM simulations give nearly identical results for exchange dynamics. However, in the larger particle simulations (256 waters) there is a significant reduction in the second shell to bulk exchanges. © 2010 American Institute of Physics.
BibTeX:
@article{Cauet2010a,
  author = {Cauët, E. and Bogatko, S. and Weare, J.H. and Fulton, J.L. and Schenter, G.K. and Bylaska, E.J.},
  title = {Structure and dynamics of the hydration shells of the Zn2+ ion from ab initio molecular dynamics and combined ab initio and classical molecular dynamics simulations},
  journal = {Journal of Chemical Physics},
  year = {2010},
  volume = {132},
  article number = {194502},
  doi = {10.1063/1.3421542}
}
Abstract: Vertical ionization potentials (IPs) of nucleobases embedded in a fully solvated DNA fragment (12-mer B-DNA fragment + 22 sodium counterions + 5760 water molecules equilibrated to 298 K) have been calculated using a combined quantum mechanical molecular mechanics (QM/MM) approach. Calculations of the vertical IP of the anion Cl- are reported that support the accuracy of the application of a QM/MM method to this problem. It is shown that the π nucleotide HOMO origin for the emitted electron is localized on the base by the hydration structure surrounding the DNA in a way similar to that recently observed for pyrimidine nucleotides in aqueous solutions (Slavícě k, P.; et al. J. Am. Chem. Soc. 2009, 131, 6460). In a first step, a high level of theory, CCSD(T)/aug-cc-pVDZ, was used to calculate the vertical IP of each of the four single bases isolated in the QM region while the remaining DNA fragment, counterions, and water solvent molecules were included in the MM region. The calculated vertical IPs show a large positive shift of 3.2-3.3 eV compared to the corresponding gas-phase values. This shift is similar for all four DNA bases. The origin of the large increase in vertical IPs of nucleobases is found to be the long-range electrostatic interactions with the solvation structure outside the DNA helix. Thermal fluctuations in the fluid can result in IP changes of roughly 1 eV on a picosecond time scale. IPs of π-stacked and H-bonded clusters of DNA bases were also calculated using the same QM/MM model but with a lower level of theory, B3LYP/6-31G(d=0.2). An IP shift of 4.02 eV relative to the gas phase is found for a four-base-pair B-DNA duplex configuration. The primary goal of this work was to estimate the influence of long-range solvation interactions on the ionization properties of DNA bases rather than provide highly precise IP evaluations. The QM/MM model presented in this work provides an attractive method to treat the difficult problem of incorporating a detailed long-range structural model of physiological conditions into investigations of the electronic processes in DNA. © 2010 American Chemical Society.
BibTeX:
@article{Cauet2010b,
  author = {Cauët, E. and Valiev, M. and Weare, J.H.},
  title = {Vertical ionization potentials of nucleobases in a fully solvated DNA environment},
  journal = {Journal of Physical Chemistry B},
  year = {2010},
  volume = {114},
  pages = {5886-5894},
  doi = {10.1021/jp9120723}
}
Abstract: Hyperfine structure parameters are calculated for the 2p2( 3P)3s 4PJ, 2p2(3P)3p 4Po J and 2p2(3P)3p 4Do J levels, using the ab initio multiconfiguration Hartree-Fock method. The theoretical hyperfine coupling constants are in complete disagreement with the experimental values of Jennerich et al deduced from the analysis of the near-infrared Doppler-free saturated absorption spectra. © 2010 IOP Publishing Ltd.
BibTeX:
@article{Joensson2010,
  author = {Jönsson, P. and Carette, T. and Nemouchi, M. and Godefroid, M.},
  title = {Ab initio calculations of 14N and 15N hyperfine structures},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2010},
  volume = {43},
  article number = {115006},
  doi = {10.1088/0953-4075/43/11/115006}
}
Abstract: Using the quantum chemistry package MOLPRO and an adapted basis set, we have calculated the adiabatic potential energy curves of the first 20 1Σ+, 19 3Σ+, 12 1Π, 9 3Π, 4 1Δ and 2 3Δ electronic states of the HeH+ molecular ion in CASSCF and CI approaches. The results are compared with previous works. The radial and rotational non-adiabatic coupling matrix elements as well as the dipole moments are also calculated. The asymptotic behaviour of the potential energy curves and of the various couplings between the states is also studied. Using the radial couplings, the diabatic representation is defined and we present an example of our diabatization procedure on the 1Σ + states. © 2010 IOP Publishing Ltd.
BibTeX:
@article{Loreau2010,
  author = {Loreau, J. and Liévin, J. and Palmeri, P. and Quinet, P. and Vaeck, N.},
  title = {Ab initio calculation of the 66 low-lying electronic states of HeH +: Adiabatic and diabatic representations},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2010},
  volume = {43},
  article number = {065101},
  doi = {10.1088/0953-4075/43/6/065101}
}
Abstract: The first metastable triplet state of HeH+ was found to be present in ion beam experiments, with its lifetime estimated to be between hundreds of milliseconds and thousand of seconds. In this work, we use ab initio methods to evaluate the radiative lifetimes of the six vibrational levels of the a 3∑+ of HeH+. The transition a 3∑+ → X1∑+ is spin-forbidden, but acquires intensity through spin-orbit interaction with the singlet and triplet Π states. Large scale CASSCF/MRCI calculations using an adapted basis set were performed to determine the potential energy curves of the relevant states of HeH+ as well as the matrix elements of the dipole and spin-orbit operators. The wave functions and energies of the vibrational levels of the a3∑+ and X1∑+ states are obtained using a B-spline method and compared to previous works. We find that the radiative lifetime of the vibrational levels increases strongly with v, the lifetime of the v=0 state being 150 s. We also analyze the contributions from discrete and continuum parts of the spectrum. With such a long lifetime, the a3∑+ state could have astrophysical implications. © 2010 American Institute of Physics.
BibTeX:
@article{Loreau2010a,
  author = {Loreau, J. and Lívin, J. and Vaeck, N.},
  title = {Radiative lifetime of the a 3∑+ + state of HeH+ from ab initio calculations},
  journal = {Journal of Chemical Physics},
  year = {2010},
  volume = {133},
  article number = {114302},
  doi = {10.1063/1.3481782}
}
Abstract: The charge-transfer in low-energy (0.25 to 150eV/amu) H(nl)+He +(1s) collisions is investigated using a quasimolecular approach for the n=2,3 as well as the first two n=4 singlet states. The diabatic potential energy curves of the HeH+ molecular ion are obtained from the adiabatic potential energy curves and the nonadiabatic radial coupling matrix elements using a two-by-two diabatization method, and a time-dependent wave-packet approach is used to calculate the state-to-state cross sections. We find a strong dependence of the charge-transfer cross section on the principal and orbital quantum numbers n and l of the initial or final state. We estimate the effect of the nonadiabatic rotational couplings, which is found to be important even at energies below 1eV/amu. However, the effect is small on the total cross sections at energies below 10eV/amu. We observe that to calculate charge-transfer cross sections in an n manifold, it is only necessary to include states with n′≤n, and we discuss the limitations of our approach as the number of states increases. © 2010 The American Physical Society.
BibTeX:
@article{Loreau2010b,
  author = {Loreau, J. and Sodoga, K. and Lauvergnat, D. and Desouter-Lecomte, M. and Vaeck, N.},
  title = {Ab initio calculation of H+He+ charge-transfer cross sections for plasma physics},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2010},
  volume = {82},
  article number = {012708},
  doi = {10.1103/PhysRevA.82.012708}
}
Abstract: We study the interconversion of multipartite symmetric N-qubit states under stochastic local operations and classical communication (SLOCC). We demonstrate that if two symmetric states can be connected with a nonsymmetric invertible local operation (ILO), then they belong necessarily to the separable, W, or Greenberger-Horne-Zeilinger (GHZ) entanglement class, establishing a practical method of discriminating subsets of entanglement classes. Furthermore, we prove that there always exists a symmetric ILO connecting any pair of symmetric N-qubit states equivalent under SLOCC, simplifying the requirements for experimental implementations of local interconversion of those states. © 2010 The American Physical Society.
BibTeX:
@article{Mathonet2010,
  author = {Mathonet, P. and Krins, S. and Godefroid, M. and Lamata, L. and Solano, E. and Bastin, T.},
  title = {Entanglement equivalence of N-qubit symmetric states},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2010},
  volume = {81},
  article number = {052315},
  doi = {10.1103/PhysRevA.81.052315}
}
Abstract: An examination is made of how the nuclear motion Hamiltonian arises from a consideration of solutions to the eigenvalue problem for the full Coulomb Hamiltonian and the role played by the usual clamped-nuclei electronic Hamiltonian in the construction of such solutions. © 2009 Springer-Verlag.
BibTeX:
@article{Sutcliffe2010,
  author = {Sutcliffe, B.},
  title = {To what question is the clamped-nuclei electronic potential the answer?},
  journal = {Theoretical Chemistry Accounts},
  year = {2010},
  volume = {127},
  pages = {121-131},
  doi = {10.1007/s00214-009-0594-0}
}
Abstract: Multiconfiguration expansions frequently target valence correlation and correlation between valence electrons and the outermost core electrons. Correlation within the core is often neglected. A large orbital basis is needed to saturate both the valence and core-valence correlation effects. This in turn leads to huge numbers of configuration state functions (CSFs), many of which are unimportant. To avoid the problems inherent to the use of a single common orthonormal orbital basis for all correlation effects in the multiconfiguration Hartree-Fock (MCHF) method, we propose to optimize independent MCHF pair-correlation functions (PCFs), bringing their own orthonormal one-electron basis. Each PCF is generated by allowing single- and double-excitations from a multireference (MR) function. This computational scheme has the advantage of using targeted and optimally localized orbital sets for each PCF. These pair-correlation functions are coupled together and with each component of the MR space through a low dimension generalized eigenvalue problem. Nonorthogonal orbital sets being involved, the interaction and overlap matrices are built using biorthonormal transformation of the coupled basis sets followed by a counter-transformation of the PCF expansions. Applied to the ground state of beryllium, the new method gives total energies that are lower than the ones from traditional complete active space (CAS)-MCHF calculations using large orbital active sets. It is fair to say that we now have the possibility to account for, in a balanced way, correlation deep down in the atomic core in variational calculations. © 2010 IOP Publishing Ltd.
BibTeX:
@article{Verdebout2010,
  author = {Verdebout, S. and Jönsson, P. and Gaigalas, G. and Godefroid, M. and Fischer, C.F.},
  title = {Exploring biorthonormal transformations of pair-correlation functions in atomic structure variational calculations},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2010},
  volume = {43},
  article number = {074017},
  doi = {10.1088/0953-4075/43/7/074017}
}
Abstract: We solve the entanglement classification under stochastic local operations and classical communication (SLOCC) for all multipartite symmetric states in the general N-qubit case. For this purpose, we introduce 2 parameters playing a crucial role, namely, the diversity degree and the degeneracy configuration of a symmetric state. Those parameters give rise to a simple method of identifying operational families of SLOCC entanglement classes of all symmetric N-qubit states, where the number of families grows as the partition function of the number of qubits. © 2009 The American Physical Society.
BibTeX:
@article{Bastin2009,
  author = {Bastin, T. and Krins, S. and Mathonet, P. and Godefroid, M. and Lamata, L. and Solano, E.},
  title = {Operational families of entanglement classes for symmetric N-qubit states},
  journal = {Physical Review Letters},
  year = {2009},
  volume = {103},
  article number = {070503},
  doi = {10.1103/PhysRevLett.103.070503}
}
Abstract: The charge transfer process in an ionized stacking of two consecutive guanines (G5'G3')+ has been studied by means of state-averaged CASSCF/MRCI and RASSCF/RASPT2 calculations. The ground and two first excited states of the radical cation have been characterized, and the topology of the corresponding potential energy surfaces (PESs) has been studied as a function of all intermolecular geometrical parameters. The results demonstrate that the charge transfer process in (G5'G 3')- is governed by the avoiding crossing between the ground and first excited states of the complex. Relative translation motions of both guanines in their molecular planes are shown to lead to the charge migration between G5' and G3'. Five stationary points (three minima and two saddle points) have been characterized along the reaction path describing the passage of the positive charge from G5' to G 3'. The global minimum on the PES is found to correspond to the charge configuration G5'+G3'. The existence of an intermediate minimum along the reaction path has been established, characterizing a structure where the positive charge is equally distributed between the two guanines. The calculated energy profile allowed us to determine the height of the potential energy barrier (7.33 kcal/mol) and to evaluate the electronic coupling at a geometry close to the avoiding crossing (3.6 kcal/mol). Test calculations showed that the topology of the ground state PES of the complex GG+ is qualitatively conserved upon optimization of the intramolecular geometrical parameters of the stationary points. © 2009 American Chemical Society.
BibTeX:
@article{Caueet2009,
  author = {Cauëet, E. and Liévin, J.},
  title = {Ab initio study of the electron transfer in an ionized stacked complex of guanines},
  journal = {Journal of Physical Chemistry A},
  year = {2009},
  volume = {113},
  pages = {9881-9890},
  doi = {10.1021/jp902426p}
}
Abstract: A quantitative characterization of the Rydberg and valence singlet electronic states of acetylene lying in the 5-10.7 eV region is performed by using large-scale ab initio calculations. A special attention is paid on the comparison between the present calculations and Mulliken's concepts for Rydberg states, based on singleelectron and single-configuration description. Most of the properties of the Rydberg states have been qualitatively understood via this comparison, mainly shown by the shape and size of the outer Rydberg molecular orbital. More quantitatively, Rydberg-valence mixing has been evaluated in several excited energy regions, as for instance, the interaction between the C̃ ' (1πg)2 1Ag doubly excited valence state and the manifold of electronic components of the np series, or the interaction between the Ẽ 1πg 1Bu valence state and the F̃ 3dπg 1σu + Rydberg state. The rapid predissociation of the lowest C̃ 3só 1.u Rydberg state has been interpreted as a case of Rydbergization, earlier predicted by Mulliken. © 2009 American Chemical Society.
BibTeX:
@article{Laruelle2009,
  author = {Laruelle, F. and Boyé-Péronne, S. and Gauyacq, D. and Liévin, J.},
  title = {Revisiting mulliken's concepts about rydberg states and rydberg-valence interactions from large-scale ab initio calculations on the acetylene molecule},
  journal = {Journal of Physical Chemistry A},
  year = {2009},
  volume = {113},
  pages = {13210-13220},
  doi = {10.1021/jp903948k}
}
Abstract: New theoretical and experimental results on the acetylene-Ar van der Waals complex are presented and the literature is reviewed. New ab initio calculations at the MP2 level were performed using large basis sets with diffuse functions and taking into account the basis set superposition error. It was found that the structure of acetylene is not significantly altered by the complexation and that its vibrational frequencies are only slightly lowered. Finally, it was observed that the calculated properties of the complex (structure, vibrational spectrum, bond dissociation energy) are not sensitive to the structure imposed on acetylene. Experimentally, acetylene-Ar was produced in a supersonic expansion under experimental conditions corresponding to 9 K rotational temperature. Thanks to the performances of CW-CRDS detection, the Ka = 0 ← 1, 1 ← 0, and 2 ← 1 sub- bands of the v1 + v3 band could be recorded and resolved and most of their lines assigned. Upper-state rotational constants were fitted, however not including the upper Ka = 2 state, which shows K-doubling the opposite of the expected. The Lorentzian width of most line profiles sets the mean lifetime to some 7.5 ns. Local perturbations affecting line positions and/or line widths are demonstrated. Additional series of lines tentatively attributed to acetylene-Ar are discussed.© 2009 American Chemical Society.
BibTeX:
@article{Lauzin2009,
  author = {Lauzin, C. and Didriche, K. and Macko, P. and Demaison, J. and Lievin, J. and Herman, M.},
  title = {12C2H2-Ar van der Waals complex},
  journal = {Journal of Physical Chemistry A},
  year = {2009},
  volume = {113},
  pages = {2359-2365},
  doi = {10.1021/jp8077908}
}
Abstract: The relativistic corrections to the magnetic dipole moment operator in the Pauli approximation were derived originally by Drake (1971 Phys. Rev. A 3 908). In the present paper, we derive their irreducible tensor-operator form to be used in atomic structure codes adopting the Fano-Racah-Wigner algebra for calculating its matrix elements. © 2009 IOP Publishing Ltd.
BibTeX:
@article{Nemouchi2009,
  author = {Nemouchi, M. and Godefroid, M.R.},
  title = {Irreducible tensor form of the relativistic corrections to the M1 transition operator},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2009},
  volume = {42},
  article number = {175002},
  doi = {10.1088/0953-4075/42/17/175002}
}
Abstract: Emission spectra of WO have been observed in the 4000-35 000 cm-1 region using a Fourier transform spectrometer. Molecules were produced by exciting a mixture of WCl6 vapor and He in a microwave discharge lamp. A 3Σ- state has been assigned as the ground state of WO based on a rotational analysis of the observed bands and ab initio calculations. After rotational analysis, a majority of strong bands have been classified into three groups. Most of the transitions belonging to the first group have an Ω = 0+ state as the lower state while the bands in the second group have an Ω′′ = 1 state as the lower state. These two lower states have been assigned as X0+ and X1 spin components of the X3Σ- ground state of WO. The third group consists of additional bands interconnected by common vibrational levels involving some very low-lying states. The spectroscopic properties of the low-lying electronic states have been predicted from ab initio calculations. The details of the rotational analysis are presented and an attempt has been made to explain the experimental observations in the light of the ab initio results. © 2009 Elsevier Inc. All rights reserved.
BibTeX:
@article{Ram2009,
  author = {Ram, R.S. and Liévin, J. and Bernath, P.F.},
  title = {Fourier transform emission spectroscopy and ab initio calculations on WO},
  journal = {Journal of Molecular Spectroscopy},
  year = {2009},
  volume = {256},
  pages = {216-227},
  doi = {10.1016/j.jms.2009.04.010}
}
Abstract: The total and partial photodissociation cross sections of the molecular ion HeH+ are computed by time-dependent methods for fragmentation into the excited shells n=1,2,3 up to a photon energy of 40 eV. Σ1 + and Π1 states are considered for parallel and perpendicular transitions for different initial rotational or vibrational excitations. Nonadiabatic radial and rotational couplings are taken into account. The results from coupled-channel equations are compared with the Born-Oppenheimer approximation. A time-dependent calculation with a femtosecond laser pulse is carried out to simulate a recent crossed beam photodissociation imaging experiment with vacuum ultraviolet free-electron laser. The dominance of photodissociation perpendicular to the photon polarization is confirmed. © 2009 The American Physical Society.
BibTeX:
@article{Sodoga2009,
  author = {Sodoga, K. and Loreau, J. and Lauvergnat, D. and Justum, Y. and Vaeck, N. and Desouter-Lecomte, M.},
  title = {Photodissociation of the HeH+ ion into excited fragments (n=2,3) by time-dependent methods},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2009},
  volume = {80},
  article number = {033417},
  doi = {10.1103/PhysRevA.80.033417}
}
Abstract: The vibrational energy levels of fluoroform have been computed with and without the kinetic coupling terms of the Eckart-Watson Hamiltonian by using the vibrational mean field configuration interaction method. The results are well-converged as demonstrated by a comparison with those obtained with other variational methods when kinetic coupling is omitted. It is found that kinetic coupling is not negligible for this system. The wave number difference with and without kinetic coupling is 37 cm-1 for the ν1 (CH-stretching) fundamental transition and can be larger than 60 cm-1 in the ν1 s(-) ν4 (HCF bending) overtones. © 2008 Elsevier B.V. All rights reserved.
BibTeX:
@article{Cassam-Chenai2008,
  author = {Cassam-Chenaï, P. and Scribano, Y. and Liévin, J.},
  title = {Influence of kinetic coupling in rectilinear coordinates on the vibrational spectrum of fluoroform},
  journal = {Chemical Physics Letters},
  year = {2008},
  volume = {466},
  pages = {16-20},
  doi = {10.1016/j.cplett.2008.10.025}
}
Abstract: The equilibrium structure of the hydrogen bonded complex H2O HF has been calculated ab initio using the CCSD(T) method with basis sets up to sextuple- quality with diffuse functions and taking into account the basis set superposition error correction. The calculations carried out confirm the importance of diffuse functions and of counterpoise correction to obtain an accurate geometry. The most important point is that the basis set convergence is extremely slow and, for this reason an accurate ab initio structure requires a very large basis set. Nevertheless, the ab initio structure is significantly different from the experimental r0 and rm structures. Analysis of the basis set convergence and of the approximations used for the determination of the experimental structures indicates that the ab initio structure is expected to be more reliable.
BibTeX:
@article{Demaison2008a,
  author = {Demaison, J. and Lievin, J.},
  title = {Equilibrium structure of the hydrogen bonded dimer H2O ⋯ HF},
  journal = {Molecular Physics},
  year = {2008},
  volume = {106},
  pages = {1249-1256},
  doi = {10.1080/00268970802139908}
}
Abstract: Born-Oppenheimer equilibrium structures, reBO, of the electronic ground state of the borazane (BH3NH3) molecule of C3v., point-group symmetry are computed ab initio using the CCSD(T) method with basis sets up to quintuple-ζ quality. Inclusion of the counterpoise correction and extrapolation of the structural parameters to the complete basis set limit yield a best estimate of reBO of BH3NH3. The anharmonic force field of BH 3NH3, computed at the CCSD(T) level of theory with a basis set of triple-ζ quality, allows the determination of semi-experimental equilibrium rotational constants, which in turn result in a semi-experimental equilibrium structure, reSE. The re BO and reSE structures are in excellent agreement, indicating the validity of the methods used for their determination. The empirical mass-dependent structure, rm(1), of BH 3NH3 is also determined. Although it is inferior in quality to the previous two structures, it is much more accurate than the standard empirical r0 and rs structures reported earlier for BH3NH3. The semi-experimental re SE as well as the empirical rm(1) structures determined are based on experimental ground-state rotational constants available from the literature for nine isotopologues of borazane. The effective barrier to the internal rotation of BH3NH3, a molecule isoelectronic with CH3CH3, has been computed ab initio, employing the focal-point analysis (FPA) approach, to be 699 ±11 cm -1. This compares favorably with an empirical redetermination of the effective barrier based on the above reSE structure, V3 = 718(17) cm-1. © 2008 American Chemical Society.
BibTeX:
@article{Demaison2008,
  author = {Demaison, J. and Liévin, J. and Császár, A.G. and Gutle, C.},
  title = {Equilibrium structure and torsional barrier of BH3NH3},
  journal = {Journal of Physical Chemistry A},
  year = {2008},
  volume = {112},
  pages = {4477-4482},
  doi = {10.1021/jp710630j}
}
Abstract: Absolute integral cross sections have been measured for associative ionization reactions involving the C- and C+, N+, and O+ reactants. These measurements, obtained using a merged-beam setup in the keV range, provide us with useful experimental information on the efficiency and mechanisms of molecular ion formation from ionic reactants. The relative magnitudes of the different cross sections are rationalized by considering the spin multiplicities of initial and final states, and the exothermicities of the detachment and transfer ionization channels. The very different production efficiencies of C O+ ions via the O- + C+ and C- + O+ channels are explained by statistical and energetic considerations. The potential energy curves of CO and C O+ have been calculated by quantum ab initio methods in order to characterize the reactive pathways leading to autoionization. Thermal rate coefficients are derived to serve the plasma physics community. © 2008 The American Physical Society.
BibTeX:
@article{LePadellec2008,
  author = {Le Padellec, A. and Liévin, J. and Staicu-Casagrande, E.M. and Nzeyimana, T. and Naji, E.A. and Urbain, X.},
  title = {Competitive processes in the associative ionization of C- with C+, N+, and O+},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2008},
  volume = {78},
  article number = {062705},
  doi = {10.1103/PhysRevA.78.062705}
}
BibTeX:
@article{Sutcliffe2008a,
  author = {Sutcliffe, B.},
  title = {Risk aversion},
  journal = {Chemistry World},
  year = {2008},
  volume = {5},
  pages = {40}
}
Abstract: An attempt is made to determine the relationship between the full Schrödinger Coulomb Hamiltonian and the clamped nuclei form that is usually the basis of electronic structure calculations, without treating identical nuclei as distinguishable. It is concluded that it is not at present possible to establish such a relationship in a mathematically secure way. © 2008 Springer Science+Business Media, LLC.
BibTeX:
@article{Sutcliffe2008,
  author = {Sutcliffe, B.T.},
  title = {What mathematicians know about the solutions of Schrodinger Coulomb Hamiltonian. Should chemists care?},
  journal = {Journal of Mathematical Chemistry},
  year = {2008},
  volume = {44},
  pages = {988-1008},
  doi = {10.1007/s10910-008-9358-7}
}
Abstract: Two recently developed methods for solving the molecular vibrational Schrödinger equation, namely, the parallel vibrational multiple window configuration interaction and the vibrational mean field configuration interaction, are presented and compared on the same potential energy surface of ethylene oxide, c-C2H4O. It is demonstrated on this heptatomic system with strong resonances that both approaches converge towards the same fundamental frequencies. This confirms their ability to tackle the vibrational problem of large molecules for which full configuration interaction calculations are not tractable. © 2007 American Institute of Physics.
BibTeX:
@article{Begue2007,
  author = {Bégué, D. and Gohaud, N. and Pouchan, C. and Cassam-Chenai, P. and Liévin, J.},
  title = {A comparison of two methods for selecting vibrational configuration interaction spaces on a heptatomic system: Ethylene oxide},
  journal = {Journal of Chemical Physics},
  year = {2007},
  volume = {127},
  article number = {164115},
  doi = {10.1063/1.2795711}
}
Abstract: A novel quantum similarity measure (QSM) is constructed based on concepts from information theory. In an application of QSM to atoms, the new QSM and its corresponding quantum similarity index (QSI) are evaluated throughout the periodic table, using the atomic electron densities and shape functions calculated in the Hartree-Fock approximation. The periodicity of Mendeleev's table is regained for the first time through the evaluation of a QSM. Evaluation of the information theory based QSI demonstrates, however, that the patterns of periodicity are lost due to the renormalization of the QSM, yielding chemically less appealing results for the QSI. A comparison of the information content of a given atom on top of a group with the information content of the elements in the subsequent rows reveals another periodicity pattern. Relativistic effects on the electronic density functions of atoms are investigated. Their importance is quantified in a QSI study by comparing for each atom, the density functions evaluated in the Hartree-Fock and Dirac-Fock approximations. The smooth decreasing of the relevant QSI along the periodic table illustrates in a quantitative way the increase of relativistic corrections with the nuclear charge. © 2007 American Institute of Physics.
BibTeX:
@article{Borgoo2007,
  author = {Borgoo, A. and Godefroid, M. and Indelicato, P. and De Proft, F. and Geerlings, P.},
  title = {Quantum similarity study of atomic density functions: Insights from information theory and the role of relativistic effects},
  journal = {Journal of Chemical Physics},
  year = {2007},
  volume = {126},
  article number = {044102},
  doi = {10.1063/1.2428295}
}
Abstract: This review summarizes the contribution of high level quantum chemical calculations to the investigation of some elementary reactive processes related to the radiation damage to DNA. It is focused on the biomimetic species that govern these processes at the molecular level. These species are the DNA bases, isolated or embedded in base clusters. Their cations, formed by ionization in their ground and first excited electronic states, are at the center of the present work. We present a synthetic and critical overview of the computational methods used to predict accurate ionization potentials, to correctly describe the non-bonding interactions (stacking, H-bonding and cation-π) stabilizing the studied biomimetic clusters, to characterize their excited states and to investigate the topology of the corresponding potential energy surfaces (minima, transition states, avoided crossings, conical intersections, reaction paths). All these aspects are illustrated by the recent literature and by our own research work, namely on the electron transfer occurring within a stacked dimer of guanines. © 2007 Elsevier Inc. All rights reserved.
BibTeX:
@article{Cauet2007,
  author = {Cauët, E. and Liévin, J.},
  title = {Radical Cations of the Nucleic Bases and Radiation Damage to DNA: Ab Initio Study},
  journal = {Advances in Quantum Chemistry},
  year = {2007},
  volume = {52},
  pages = {121-147},
  doi = {10.1016/S0065-3276(06)52006-4}
}
Abstract: The Coulomb three-body problem in Jacobi coordinates was solved by treating the distance of the particles having equal charge as a parameter. This method allows computation of electronic energies with finite nuclear masses while maintaining the notion of a potential energy curve. The rotationless ground-state electronic and the so-called adiabatic Jacobi correction (AJC) energies are presented for H2+, D2+, and H D+ at fixed internuclear separations. The AJCs are defined as the difference between the results obtained from calculations using proper finite and infinite nuclear masses. Except at the united atom limit, the AJCs are smaller than the traditional first-order diagonal Born-Oppenheimer corrections. Expectation values of proton-electron, p-e, and deuteron-electron, d-e, distances for H D+ have been computed as a function of internuclear separation. Similarly to the fully nonadiabatic approach, the present method is able to follow the symmetry breaking in H D+. Exact and approximate analytical and numerical results are given for counterfactual systems as well. In these cases changes are allowed for the values of the electron rest mass or the elementary charge, as well as for the mass or charge of the unique particle (electron). © 2007 American Institute of Physics.
BibTeX:
@article{Czako2007b,
  author = {Czakó, G. and Császár, A.G. and Szalay, V. and Sutcliffe, B.T.},
  title = {Adiabatic Jacobi corrections for H2+ -like systems},
  journal = {Journal of Chemical Physics},
  year = {2007},
  volume = {126},
  article number = {024102},
  doi = {10.1063/1.2406068}
}
Abstract: A technique has been developed which in principle allows the determination of the full rotational-vibrational eigenspectrum of triatomic molecules by treating the important singularities present in the triatomic rotational-vibrational kinetic energy operator given in Jacobi coordinates and the R1 embedding. The singular term related to the diatom-type coordinate, R1, deemed to be unimportant for spectroscopic applications, is given no special attention. The work extends a previous [J. Chem. Phys., 2005, 122, 024101] vibration-only approach and employs a generalized finite basis representation (GFBR) resulting in a nonsymmetric Hamiltonian matrix [J. Chem. Phys., 2006, 124, 014110]. The basis set to be used is obtained by taking the direct product of a 1-D DVR basis, related to R 1, with a 5-D nondirect-product basis, the latter formed by coupling Bessel-DVR functions depending on the distance-type coordinate causing the singularity, associated Legendre polynomials depending on the Jacobi angle, and rotational functions depending on the three Euler angles. The robust implicitly restarted Arnoldi method within the ARPACK package is used for the determination of a number of eigenvalues of the nonsymmetric Hamiltonian matrix. The suitability of the proposed approach is shown by the determination of the rotational-vibrational energy levels of the ground electronic state of H 3+ somewhat above its barrier to linearity. Convergence of the eigenenergies is checked by an alternative approach, employing a Hamiltonian expressed in Radau coordinates, a standard direct-product basis, and no treatment of the singularities. © the Owner Societies 2007.
BibTeX:
@article{Czako2007,
  author = {Czakó, G. and Furtenbacher, T. and Barletta, P. and Császár, A.G. and Szalay, V. and Sutcliffe, B.T.},
  title = {Use of a nondirect-product basis for treating singularities in triatomic rotational-vibrational calculations},
  journal = {Annual Reports on the Progress of Chemistry - Section B},
  year = {2007},
  volume = {103},
  pages = {3407-3415},
  doi = {10.1039/b701911d}
}
Abstract: A technique has been developed which in principle allows the determination of the full rotational-vibrational eigenspectrum of triatomic molecules by treating the important singularities present in the triatomic rotational-vibrational kinetic energy operator given in Jacobi coordinates and the R(1) embedding. The singular term related to the diatom-type coordinate, R(1), deemed to be unimportant for spectroscopic applications, is given no special attention. The work extends a previous [J. Chem. Phys., 2005, 122, 024101] vibration-only approach and employs a generalized finite basis representation (GFBR) resulting in a nonsymmetric Hamiltonian matrix [J. Chem. Phys., 2006, 124, 014110]. The basis set to be used is obtained by taking the direct product of a 1-D DVR basis, related to R(1), with a 5-D nondirect-product basis, the latter formed by coupling Bessel-DVR functions depending on the distance-type coordinate causing the singularity, associated Legendre polynomials depending on the Jacobi angle, and rotational functions depending on the three Euler angles. The robust implicitly restarted Arnoldi method within the ARPACK package is used for the determination of a number of eigenvalues of the nonsymmetric Hamiltonian matrix. The suitability of the proposed approach is shown by the determination of the rotational-vibrational energy levels of the ground electronic state of H(3)(+) somewhat above its barrier to linearity. Convergence of the eigenenergies is checked by an alternative approach, employing a Hamiltonian expressed in Radau coordinates, a standard direct-product basis, and no treatment of the singularities.
BibTeX:
@article{Czako2007a,
  author = {Czakó, G. and Furtenbacher, T. and Barletta, P. and Császár, A.G. and Szalay, V. and Sutcliffe, B.T.},
  title = {Use of a nondirect-product basis for treating singularities in triatomic rotational-vibrational calculations.},
  journal = {Physical chemistry chemical physics : PCCP},
  year = {2007},
  volume = {9},
  pages = {3407-3415},
  doi = {10.1039/b701911d}
}
Abstract: The equilibrium structure of 36 small molecules containing OH bonds, including molecules with an internal hydrogen bond, is reviewed from the literature. The structures are redetermined or determined, if necessary, using high level ab initio calculations at the CCSD(T) level of theory with basis sets of quintuple zeta quality and with a correction for the core correlation. The possibility of calculating accurate ab initio OH bond lengths at different levels of theory (MP2/VTZ, MP2/VQZ, CCSD(T)/VTZ, and CCSD(T)/AVTZ) is examined. All methods agree provided a small offset correction is taken into account. In most cases, the addition of diffuse functions does not improve the results. The MP2 method appears to be satisfactory whenever the non-dynamical electron correlation is small, which is the most typical situation. The various results are merged to demonstrate the following quantitative correlation between re(OH) and 'isolated' OH stretching frequencies, relevant for predictive use: re(OH) [Å] = 1.2261(76)-7.29(21) x 10-5 νis(OH) [cm-1]. © 2007 Taylor & Francis.
BibTeX:
@article{Demaison2007a,
  author = {Demaison, J. and Herman, M. and Lievin, J.},
  title = {The equilibrium OH bond length},
  journal = {International Reviews in Physical Chemistry},
  year = {2007},
  volume = {26},
  pages = {391-420},
  doi = {10.1080/01442350701371919}
}
Abstract: The rotational spectra of the ground vibrational state and the ν9 = 1 torsional state have been reinvestigated and accurate spectroscopic constants have been determined. The torsional frequency, ν9 = 70(15) cm-1, has been determined by relative intensity measurements. The assignment of the infrared spectrum has been slightly revised and an accurate harmonic force field has been calculated. The equilibrium structure has been determined using different, complementary methods: experimental, semi-experimental and ab initio, leading to r(NN) = 1.870(2) Å, in particular. © 2007 Elsevier Inc. All rights reserved.
BibTeX:
@article{Demaison2007,
  author = {Demaison, J. and Herman, M. and Liévin, J. and Margulès, L. and Møllendal, H.},
  title = {Rotational spectrum and structure of asymmetric dinitrogen trioxide, N2O3},
  journal = {Journal of Molecular Spectroscopy},
  year = {2007},
  volume = {244},
  pages = {160-169},
  doi = {10.1016/j.jms.2007.06.003}
}
Abstract: The equilibrium structure of the more stable conformer of H 2SO4, of C2 symmetry, has been calculated ab initio using the CCSD(T) method and taking into account the core correlation correction. The accuracy of this structure has been checked by comparing it to that of similar molecules and by estimating the effects of basis set enlargement and of diffuse functions. Furthermore, the quadratic, cubic, and quartic force fields have been calculated at the MP2 level of theory using a basis set of triple-ζ quality. The spectroscopic constants derived from the force field are in satisfactory agreement with the experimental ones. The resulting band origins are compared to literature infrared values, including those for overtone and combination bands. Normal modes of vibration are pictured. Using this force field, semiexperimental equilibrium rotational constants are determined which allows us to check the accuracy of the ab initio structure and to refine it using a mixed regression method. © 2007 American Chemical Society.
BibTeX:
@article{Demaison2007b,
  author = {Demaison, J. and Herman, M. and Liévin, J. and Rudolph, H.D.},
  title = {Equilibrium structure of sulfuric acid},
  journal = {Journal of Physical Chemistry A},
  year = {2007},
  volume = {111},
  pages = {2602-2609},
  doi = {10.1021/jp068808e}
}
Abstract: An MCHF atomic-structure package is presented based on dynamic memory allocation, sparse matrix methods, and a recently developed angular library. It is meant for large-scale calculations in a basis of orthogonal orbitals for groups of LS terms of arbitrary parity. For Breit-Pauli calculations, all operators-spin-orbit, spin-other orbit, spin-spin, and orbit-orbit-may be included. For transition probabilities the orbitals of the initial and final state need not be orthogonal. A bi-orthogonal transformation is used for the evaluation of matrix elements in such cases. In addition to transition rates of all types, isotope shifts and hyperfine constants can be computed as well as gJ factors. New version summary: Title of program: atsp2K. Version number: 1.00. Catalogue identifier: ADLY_v2_0. Program summary URL: http://cpc.cs.qub.ac.uk/summaries/ADLY_v2_0. Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland. Computer: Pentium III 500 MHz. Installations: Vanderbilt University, Nashville, TN 37235, USA. Operating systems under which the present version has been tested: Red Hat 8. Programming language used in the present version: FORTRAN 90. Memory required to execute with typical data: 256 Mbytes words. No. of bits in a word: 32. Supplementary material: User manuals for the program atsp2k and for the Spin-Angular library are available. No. of lines in distributed program, including test data, etc.:209 992. No. of bytes in distributed package, including test data, etc.: 1 740 883. Distribution format: tar.gz. CPC Program Library subprograms used: none. Does the new version supersede the previous version?: Yes. Nature of physical problem: This program determines energy levels and associated wave functions for states of atoms and ions in the MCHF (LS) or Breit-Pauli (LSJ) approximation. Given the wave function, various atomic properties can be computed such as electric (Ek) and magnetic (Mk) multipole radiative transition probabilities (kmax = 10) between LS or LSJ states, isotope shift constants, hyperfine parameters, and gJ factors. Method of solution: The new version of the program closely follows the design and structure of the previous one [C. Froese Fischer, Comput. Phys. Comm. 128 (2000) 635], except that a simultaneous optimization scheme has been introduced. This program uses the angular methodology of [G. Gaigalas, Lithuanian J. Phys. 41 (2000) 39] and has been extended to include partially filled f-subshells in wavefunction expansions but assumes all orbitals are orthonormal. The bi-orthogonal transformation method is used to deal with the non-orthogonality of orbitals between initial and final states of an electromagnetic radiative transition. Reasons for new version: The previous version of the MCHF atomic structure package [C. Froese Fischer, Comput. Phys. Comm. 128 (2000) 635] was intended for small calculations, ideal for someone not familiar with the code, producing extensive print-out of intermediate results. The codes for the calculation of spin-angular coefficients were often not the most efficient and could only treat configurations with open f-subshells containing at most two electrons or an almost filled shell with one hole. The present version is designed for large-scale computation using algorithms for angular integration that have been shown to be faster, and include the case of arbitrarily filled f-shells. In addition, the MCHF program has been modified to include optimization on an energy functional that is a weighted average of energy functionals for expansions of wavefunctions for different LS terms or parity, thus facilitating Breit-Pauli calculations for complex atomic systems and for computing targets in collision calculations. Summary of revisions: Programs have been modified to take advantage of the newly developed angular library [G. Gaigalas, Lithuanian J. Phys. 41 (2000) 39], extended to arbitrarily filled f-shells. New programs have been developed for simultaneous optimization and for the efficient calculation of atomic spectra and transition rates for an iso-electronic sequence. All applications now take advantage of dynamic memory allocation and sparse matrix methods. Restrictions on the complexity of the problem: All orbitals in a wave function expansion are assumed to be orthonormal. Configuration states are restricted to at most eight (8) subshells in addition to the closed shells common to all configuration states. The maximum size is limited by the available memory and disk space. Typical running time: Included with the code are scripts for calculating E2 and M1 transitions between levels of 3 s2 3 p2 for Si and P+. This calculation has two stages: LS and LSJ. The calculation of the former required 21 minutes for the LS calculation and 36.5 minutes for the Breit-Pauli configuration interaction calculation that determines the mixing of the terms. Unusual features of the program: The programming style is essentially F77 with extensions for the POINTER data type and associated memory allocation. These have been available on workstations for more than a decade but their implementations are compiler dependent. The present serial code has been installed and tested extensively using both the Portland Group, pgf90, compiler and the IBM SP2, xlf90, compiler. The former is compatible also with the Intel Fortran90 compiler. The MPI codes are included for completeness though testing has not been as extensive. Additional comments: Parallel versions (MPI) of the following programs are included in the distribution. Use of these is optional but can speed up the angular integration processing. A table is presented. © 2007 Elsevier B.V. All rights reserved.
BibTeX:
@article{FroeseFischer2007,
  author = {Froese Fischer, C. and Tachiev, G. and Gaigalas, G. and Godefroid, M.R.},
  title = {An MCHF atomic-structure package for large-scale calculations},
  journal = {Computer Physics Communications},
  year = {2007},
  volume = {176},
  pages = {559-579},
  doi = {10.1016/j.cpc.2007.01.006}
}
Abstract: An effective and general algorithm is suggested for variational vibrational calculations of N -atomic molecules using orthogonal, rectilinear internal coordinates. The protocol has three essential parts. First, it advocates the use of the Eckart-Watson Hamiltonians of nonlinear or linear reference configuration. Second, with the help of an exact expression of curvilinear internal coordinates (e.g., valence coordinates) in terms of orthogonal, rectilinear internal coordinates (e.g., normal coordinates), any high-accuracy potential or force field expressed in curvilinear internal coordinates can be used in the calculations. Third, the matrix representation of the appropriate Eckart-Watson Hamiltonian is constructed in a discrete variable representation, in which the matrix of the potential energy operator is always diagonal, whatever complicated form the potential function assumes, and the matrix of the kinetic energy operator is a sparse matrix of special structure. Details of the suggested algorithm as well as results obtained for linear and nonlinear test cases including H2 O, H3+, C O2, HCNHNC, and C H4 are presented. © 2007 American Institute of Physics.
BibTeX:
@article{Matyus2007,
  author = {Mátyus, E. and Czakó, G. and Sutcliffe, B.T. and Császár, A.G.},
  title = {Vibrational energy levels with arbitrary potentials using the Eckart-Watson Hamiltonians and the discrete variable representation},
  journal = {Journal of Chemical Physics},
  year = {2007},
  volume = {127},
  article number = {084102},
  doi = {10.1063/1.2756518}
}
BibTeX:
@article{Sutcliffe2007a,
  author = {Sutcliffe, B.T.},
  title = {Concluding remarks},
  journal = {Faraday Discussions},
  year = {2007},
  volume = {135},
  pages = {503-506},
  doi = {10.1039/b613462a}
}
Abstract: The Schrödinger Coulomb Hamiltonian for electronic and nuclear motion in a diatomic molecule is presented and its effect upon functions which are products of functions of electronic and of nuclear variables is explicitly exhibited. Computational approaches to finding approximate solutions in such a basis are outlined. © 2007 Springer-Verlag.
BibTeX:
@article{Sutcliffe2007,
  author = {Sutcliffe, B.T.},
  title = {The separation of electronic and nuclear motion in the diatomic molecule},
  journal = {Theoretical Chemistry Accounts},
  year = {2007},
  volume = {118},
  pages = {563-571},
  doi = {10.1007/s00214-007-0357-8}
}
Abstract: The energies of the Al Auger KL2,3L2,3 transitions and the Al 2p photoelectron peak have been determined experimentally by AES, XPS and XAES for several Al compounds. The experimental results are compared with ab initio calculations based on a cluster model in which a central aluminum atom is surrounded by its first neighbours in the crystal. This model includes chemical, structural and relaxation effects and it allows the direct ab initio determination of the intra- and extra-atomic relaxation energies. These values are compared with the Wagner equation that relates the extra-atomic relaxation energy and the Auger parameter. The three approximations that support this equation are examined on the basis of the cluster results. © 2007 Elsevier B.V. All rights reserved.
BibTeX:
@article{Timmermans2007,
  author = {Timmermans, B. and Reniers, F. and Weightman, P. and Vaeck, N.},
  title = {Auger and photoelectron relaxation energy in aluminum compounds: A cluster model},
  journal = {Journal of Electron Spectroscopy and Related Phenomena},
  year = {2007},
  volume = {159},
  pages = {1-7},
  doi = {10.1016/j.elspec.2007.01.004}
}
Abstract: The planar isomerization routes of the vinylidene/acetylene cation in the lowest electronic states are accurately examined for the first time, by using large scale MRCI and CCSD(T) calculations in a complementary way. They are compared with the similar calculations performed for the neutral ground state isomerization. An accurate value of the adiabatic ionization potential of vinylidene (11.26 eV) is predicted. The vinylidene cation lowest state, 1 A12, follows an almost flat pathway with a shallow secondary minimum on the 1 A′2 potential energy surface, before suddenly dropping to the stable acetylene cation ground state, X̃ Πu2. It is therefore confirmed to be completely unstable with respect to isomerization. The first excited state of the vinylidene cation, 1 B12, which also correlates with the Πu2 ground state of acetylene cation along a A′2 isomerization route, has been studied at the same level of calculation. This 1 B12 state is lying only 0.15 eV above the 1 A12 state, and exhibits a potential energy barrier of 0.55 eV which explains the earlier assignment of this symmetry to the ground state of vinylidene cation. In addition to large scale calculations, a comprehensive description of the important steps of isomerization drawn from a very simple model involving monoconfigurational states is presented. In particular, the behavior of one unique orbital, namely, the 5 a1 outer molecular orbital, is shown to completely govern the molecular geometry and energy evolution along the isomerization route of the ground state cation C2 H2+. © 2006 American Institute of Physics.
BibTeX:
@article{Boye-Peronne2006,
  author = {Boyé-Péronne, S. and Gauyacq, D. and Liévin, J.},
  title = {Vinylidene-acetylene cation isomerization investigated by large scale ab initio calculations},
  journal = {Journal of Chemical Physics},
  year = {2006},
  volume = {124},
  article number = {214305},
  doi = {10.1063/1.2187002}
}
Abstract: The present article introduces a general variational scheme to find approximate solutions of the spectral problem for the molecular vibration Hamiltonian. It is called the "vibrational mean field configuration interaction" (VMFCI) method, and consists in performing vibrational configuration interactions (VCI) for selected modes in the mean field of the others. The same partition of modes can be iterated until self-consistency, generalizing the vibrational self-consistent field (VSCF) method. As in contracted-mode methods, a hierarchy of partitions can be built to ultimately contract all the modes together. So, the VMFCI method extends the traditional variational approaches and can be included in existing vibrational codes based on the latter approaches. The flexibility and efficiency of this new method are demonstrated on several molecules of atmospheric interest. © 2006 Wiley Periodicals, Inc.
BibTeX:
@article{Cassam-Chenai2006,
  author = {Cassam-Chenaï, P. and Liévin, J.},
  title = {The VMFCI method: A flexible tool for solving the molecular vibration problem},
  journal = {Journal of Computational Chemistry},
  year = {2006},
  volume = {27},
  pages = {627-640},
  doi = {10.1002/jcc.20374}
}
Abstract: The ionization of the four DNA bases is investigated by means of ab initio calculations. Accurate values of the gas-phase vertical and adiabatic ionization potentials (IP) are obtained at the MP2/6-31G(2d(0.8,αd),p) level of theory. The need of introducing extra polarization to the standard 6-31G(d,p) basis set is demonstrated by test calculations and an optimal value of αd = 0.1 is obtained. Ionization to electronically excited radical cations is also considered. The low-lying excited states of the cations are characterized for the first time. The topology of the corresponding potential energy surfaces is qualitatively described in terms of the stationary points (minima and saddle points) located on these surfaces. A conical intersection is characterized for the first time on the ground-state potential energy surface of all cations. It arises from the crossing of the adiabatic surfaces of the ground and first excited state at planar geometries. A nonplanar minimum is observed for the cytosine cation only. The geometry and electronic changes occurring along these surfaces are analyzed, leading to a comparison between the different nucleobase cations. The study of larger ionized systems related to DNA is rendered possible thanks to the optimized medium size basis set proposed in this work, as exemplified by the calculation of the IP of a stacked dimer of guanines. © 2006 American Chemical Society.
BibTeX:
@article{Cauet2006,
  author = {Cauët, E. and Dehareng, D. and Liévin, J.},
  title = {Ab initio study of the lonization of the DNA bases: Ionization potentials and excited states of the cations},
  journal = {Journal of Physical Chemistry A},
  year = {2006},
  volume = {110},
  pages = {9200-9211},
  doi = {10.1021/jp0617625}
}
Abstract: The vibrational fundamentals and the rotational levels up to J=7 of the X̃3B1 and ã1A1 electronic states of CH2 have been computed completely ab initio. The calculations were based on converged, variational nuclear motion calculations employing high-quality ab initio quartic force field approximations of the related potential energy surfaces (PES). The vibrational fundamentals obtained are compared to other computational results, namely those obtained from second-order vibrational perturbation theory (VPT2) and the nonrigid-rotation- large-amplitude-internal-motion Hamiltonian (NRLH) approach. The variationally computed rotational transitions are compared both to experimentally available results and to results obtained using empirical, fitted PESs. The comparisons suggest that while the fitted PESs of X̃3B1 CH 2 reproduce excellently the available rovibrational transition wavenumbers, the corresponding stretching fundamental term values, which have not been determined experimentally, are less accurate than the ab initio values obtained in the present study. This means that the zero-point energy (ZPE) computed ab initio in the present work is an improvement over that computed from the fitted PES of X̃3B1 CH2. No similar problems are observed for the semirigid ã1A1 state of CH2, where the computed, the fitted, and the experimental results all agree with each other. The symmetric and antisymmetric stretching fundamentals of X̃3B1 CH2 obtained in this study are 3035±7 and 3249±7 cm-1, respectively. The corresponding ZPE of X̃3B1 is 3733±10 cm -1, while that of ã1A1 CH2 is 3605±15 cm-1. © 2005 Elsevier B.V. All rights reserved.
BibTeX:
@article{Furtenbacher2006,
  author = {Furtenbacher, T. and Czakó, G. and Sutcliffe, B.T. and Császár, A.G. and Szalay, V.},
  title = {The methylene saga continues: Stretching fundamentals and zero-point energy of X̃3 B1 CH2},
  journal = {Journal of Molecular Structure},
  year = {2006},
  volume = {780-781},
  pages = {283-294},
  doi = {10.1016/j.molstruc.2005.06.052}
}
Abstract: Wave packet simulations using ab initio potential energy surfaces (PES) have been developed within the framework of the constrained Hamiltonian methodology. The approach is presented with the example of bromoacetyl chloride photodissociation. © 2005 Wiley Periodicals, Inc.
BibTeX:
@article{Lasorne2006,
  author = {Lasorne, B. and Bacchus-Montabonel, M.C. and Vaeck, N. and Desouter-Lecomte, M.},
  title = {Quantum dynamics simulations of photodissociation reactions},
  journal = {International Journal of Quantum Chemistry},
  year = {2006},
  volume = {106},
  pages = {670-675},
  doi = {10.1002/qua.20829}
}
Abstract: The rotational spectrum of bromoacetyl chloride, BrCH2COCl, has been assigned using a pulsed molecular beam Fourier transform microwave spectrometer. It has been possible to determine the rotational and quartic centrifugal distortion constants of the energetically favoured conformer (anti-periplanar) as well as the complete bromine and chlorine quadrupole coupling tensors including their off diagonal elements for the following isotopomers: 79BrCH2CO35Cl, 81BrCH2CO35Cl, 79BrCH 2CO37Cl, and 81BrCH2CO 37Cl. Experimental results are supported by quantum chemical calculations. © 2005 Elsevier B.V. All rights reserved.
BibTeX:
@article{Merke2006,
  author = {Merke, I. and Vaeck, N. and Petitprez, D. and Wlodarczak, G.},
  title = {The rotational spectrum of bromoacetyl chloride},
  journal = {Journal of Molecular Structure},
  year = {2006},
  volume = {780-781},
  pages = {306-309},
  doi = {10.1016/j.molstruc.2005.06.040}
}
Abstract: The development of the idea of a potential energy surface is examined in the context of solutions to the full quantum mechanical problem specified by the Schrödinger Coulomb Hamiltonian expressed in laboratory-fixed coordinates.
BibTeX:
@article{Sutcliffe2006,
  author = {Sutcliffe, B.T.},
  title = {The idea of a potential energy surface},
  journal = {Molecular Physics},
  year = {2006},
  volume = {104},
  pages = {715-722},
  doi = {10.1080/00268970500418059}
}
Abstract: His-aromatic complexes, with the His located above the aromatic plane, are stabilized by π-π, δ+-π and/or cation-π interactions according to whether the His is neutral or protonated and the partners are in stacked or T-shape conformations. Here we attempt to probe the relative strength of these interactions as a function of the geometry and protonation state, in gas phase, in water and protein-like environments (acetone, THF and CCl4), by means of quantum chemistry calculations performed up to second order of the Møller-Plesset pertubation theory. Two sets of conformations are considered for that purpose. The first set contains 89 interactions between His and Phe, Tyr, Trp, or Ade, observed in X-ray structures of proteins and protein-ligand complexes. The second set contains model structures obtained by moving an imidazolium/imida-zole moiety above a benzene ring or an adenine moiety. We found that the protonated complexes are much more stable than the neutral ones in gas phase. This higher stability is due to the electrostatic contributions, the electron correlation contributions being equally important in the two forms. Thus, π-π and δ+-π interactions present essentially favorable electron correlation energy terms, whereas cation-π interactions feature in addition favorable electrostatic energies. The pro-tonated complexes remain more stable than the neutral ones in protein-like environments, but the difference is drastically reduced. Furthermore, the T-shape conformation is undoubtedly more favorable than the stacked one in gas phase. This advantage decreases in the solvents, and the stacked conformation becomes even slightly more favorable in water. The frequent occurrence of His-aromatic interactions in catalytic sites, at protein-DNA or protein-ligand interfaces and in 3D domain swapping proteins emphasize their importance in biological processes. © 2005 American Chemical Society.
BibTeX:
@article{Cauet2005,
  author = {Cauët, E. and Rooman, M. and Wintjens, R. and Liévin, J. and Biot, C.},
  title = {Histidine-aromatic interactions in proteins and protein-ligand complexes: Quantum chemical study of X-ray and model structures},
  journal = {Journal of Chemical Theory and Computation},
  year = {2005},
  volume = {1},
  pages = {472-483},
  doi = {10.1021/ct049875k}
}
Abstract: Ab initio multiconfiguration calculations are performed for the oscillator strengths of the λ = 4238, 4262 and 4297 Å Tc I resonance lines of astrophysical interest. Electron correlation is treated through multiconfiguration expansions built from elaborate correlation models, while relativistic effects are introduced in the perturbation Breit-Pauli approximation or in the multiconfiguration Dirac-Fock-Breit variational approach. The calculated gf-values are sensitively lower (≈30 per cent) than the values obtained with the pseudo-relativistic Hartree-Fock wavefunctions calculated from a parametric analysis of Tc I by Palmeri & Wyart. The inclusion of a core-polarization potential in the latter approach confirms the present ab initio results when different ionic cores are used for the different transition arrays. The strong lines of Tc I are revisited adopting this model, giving rise to a systematic reduction in the oscillator strength scale due to core polarization. The astrophysical implications are discussed. © 2005 RAS.
BibTeX:
@article{Palmeri2005,
  author = {Palmeri, P. and Fischer, C.F. and Wyart, J.-F. and Godefroid, M.R.},
  title = {Oscillator strength calculations in neutral technetium},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {2005},
  volume = {363},
  pages = {452-458},
  doi = {10.1111/j.1365-2966.2005.09410.x}
}
Abstract: In a paper published in 1985 (Katriel J., Paldus J., Pauncz R.: Int. J. Quantum Chem. 1985, 28, 181) Paldus and his colleagues considered explicit relations between the permutational symmetry and the spin operators for systems of identical particles. The principal concern of this paper was with particles for which σ = 1/2 but there is some consideration of the case of particles for which σ = 1. This latter consideration was developed by Katriel (Katriel J.: J. Mol. Struct. (THEOCHEM) 2001, 547, 1) in a paper honouring Prof. Paldus on the occasion of his 65th birthday. The present paper attempts a consideration of aspects of permutational symmetry, not explicitly considered in those two papers, as they affect the interpretation of the results of molecular structure calculations.
BibTeX:
@article{Sutcliffe2005d,
  author = {Sutcliffe, B.},
  title = {Permutational symmetry and molecular structure calculations},
  journal = {Collection of Czechoslovak Chemical Communications},
  year = {2005},
  volume = {70},
  pages = {657-676},
  doi = {10.1135/cccc20050657}
}
BibTeX:
@article{Sutcliffe2005b,
  author = {Sutcliffe, B.T.},
  title = {Victor Ronald Saunders: Upon his retirement from Daresbury Lab},
  journal = {Molecular Physics},
  year = {2005},
  volume = {103},
  pages = {2461-2463},
  doi = {10.1080/00268970500178802}
}
Abstract: In moving-nuclei calculations on some simple diatomics and on water, Nakai [J. Chem. Phys.122, 164101 (2005)] extend their earlier translation-free nuclear orbital plus molecular orbital (TF-NOMO) theory, in which the translational part of the Hamiltonian is subtracted from the full Hamiltonian, to a translation- and rotation-free approach, in which a rotational term is subtracted from the TF-NOMO Hamiltonian. It is suggested that the chosen rotational term is not unique and is not valid over all regions of space. © 2005 American Institute of Physics.
BibTeX:
@article{Sutcliffe2005,
  author = {Sutcliffe, B. and Nakai, H. and Hoshino, M. and Miyamoto, K. and Hyodo, S.-A.},
  title = {Comment on "elimination of translational and rotational motions in nuclear orbital plus molecular orbital theory" [J. Chem. Phys. 122, 164101 (2005)]},
  journal = {Journal of Chemical Physics},
  year = {2005},
  volume = {123},
  article number = {237101},
  doi = {10.1063/1.2134699}
}
Abstract: A recent Letter has proposed a method for obtaining molecular structures of small polyatomic molecules without recourse to the Born-Oppenheimer approximation. In this Comment we highlight the difficulties in the proposed strategy when identifying molecular structures in general. © 2005 Elsevier B.V. All rights reserved.
BibTeX:
@article{Sutcliffe2005c,
  author = {Sutcliffe, B.T. and Woolley, R.G.},
  title = {Comment on 'Molecular structure in non-Born-Oppenheimer quantum mechanics'},
  journal = {Chemical Physics Letters},
  year = {2005},
  volume = {408},
  pages = {445-447},
  doi = {10.1016/j.cplett.2005.04.022}
}
Abstract: A number of recent papers have considered ways in which molecular structure may be calculated when both the electrons and the nuclei are treated from the outset as quantum particles. This is in contrast to the conventional approach in which the nuclei initially have their positions fixed and so merely provide a potential for electronic motion. The usual approach is generally assumed to be justified by the 1927 work of Born and Oppenheimer. In this paper we discuss what precisely might be anticipated in the way of molecular structure from a mathematical consideration of the spectral properties of the full Coulomb Hamiltonian, to what extent the very idea of molecular structure might be dependent upon treating the nuclei simply as providing a potential and the extent to which the work of Born and Oppenheimer can be used to support this position. © The Owner Societies 2005.
BibTeX:
@article{Sutcliffe2005a,
  author = {Sutcliffe, B.T. and Woolley, R.G.},
  title = {Molecular structure calculations without clamping the nuclei},
  journal = {Physical Chemistry Chemical Physics},
  year = {2005},
  volume = {7},
  pages = {3664-3676},
  doi = {10.1039/b509723c}
}
Abstract: In this Letter Quantum Similarity for Atoms (H-Xe) is investigated using electron densities and shape functions, looking for patterns of periodicity as in Mendeleev's Table. An LS-dependent restricted Hartree-Fock method is used to obtain the wave functions from which the electron densities are calculated. Utilizing the quantum similarity proposed by Carbó a nearest neighbour dominated similarity is retrieved, masking periodicity. Introduction of the information discrimination concept with reference to the noble gas atom of the previous row is found to reveal periodicity, with improved results when densities are replaced by shape functions throughout. This confirms recent literature on the fundamental role of the shape function as carrier of information. © 2004 Elsevier B.V. All rights reserved.
BibTeX:
@article{Borgoo2004,
  author = {Borgoo, A. and Godefroid, M. and Sen, K.D. and De Proft, F. and Geerlings, P.},
  title = {Quantum similarity of atoms: A numerical Hartree-Fock and Information Theory approach},
  journal = {Chemical Physics Letters},
  year = {2004},
  volume = {399},
  pages = {363-367},
  doi = {10.1016/j.cplett.2004.10.026}
}
Abstract: Wave packet simulations have shown that the preferential breaking of the C-Cl bond versus the weaker C-Br one can be explained by nonadiabatic interactions at avoided crossings in both C-O/C-Br and C-O/C-Cl subspaces leading to a stronger trapping of the C-Br population. However, the branching ratio obtained by propagating wave packets in the two 2D subspaces was very satisfactory and permits not to discard this explanation. It was found that the results were in better agreement with the experimental branching ratio in 2D than in 1D.
BibTeX:
@article{Lasorne2004,
  author = {Lasorne, B. and Bacchus-Montabonel, M.-C. and Vaeck, N. and Desouter-Lecomte, M.},
  title = {Nonadiabatic interactions in wave packet dynamics of the bromoacetyl chloride photodissociation},
  journal = {Journal of Chemical Physics},
  year = {2004},
  volume = {120},
  pages = {1271-1278},
  doi = {10.1063/1.1633759}
}
Abstract: The study of the isotope shift in the electron affinity is interesting for probing correlation effects. Experiments that allow this property to be measured are rare, being difficult to realize, while accurate calculations remain a challenge for atomic theory. The present work focuses on the theoretical estimation of the isotope shift in the electron affinity of Be (2s2p 3Po), using correlated electronic wavefunctions obtained from multiconfiguration Hartree-Fock and configuration interaction variational calculations. The reliability of the correlation models is assessed from a comparison between the observed and theoretical electron affinities, and between theoretical isotope shift values for the 2s2p 3P o-2s2 1S transition of neutral beryllium. The sign and the magnitude of the difference between the mass polarization term expectation values obtained for the neutral atom and the negative ion are such that the resulting irsotope shift in the electron affinity is 'anomalous', corresponding to a smaller electron affinity for the heavier isotope.
BibTeX:
@article{Nemouchi2004,
  author = {Nemouchi, M. and Taleb, A. and Godefroid, M.},
  title = {Isotope shift in the electron affinity of beryllium},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2004},
  volume = {37},
  pages = {865-874},
  doi = {10.1088/0953-4075/37/4/013}
}
Abstract: The emission spectrum of NbCl has been recorded in the 3000-20000cm -1 region using a Fourier transform spectrometer. The bands were observed by microwave excitation of a mixture of NbCl5 vapor and He. Two groups of bands observed in the 6500-7000cm-1 and 9800-11000cm-1 regions have been assigned to two electronic transitions. Five bands observed in the 6500-7000cm-1 region consist of R, P, and Q branches with no combination defect or Λ-doubling. They have been assigned as five sub-bands of a ΔΛ=±1 transition with Λ1. Nine bands observed in the 9800-11000cm-1 regions consist of R and P branches, and they are also free from Λ-doubling. These bands have been classified into four sub-bands of a ΔΛ=0 transition (with Λ1), which has tentatively been assigned as 5Δ-5Δ. The two transitions have no electronic states in common. Ab initio calculations have been performed on NbCl and the spectroscopic properties of the low-lying electronic states have been calculated. The ground state of NbCl has been predicted to be a 5Π state arising from the 3σ1 1δ 2 2π1 configuration, with a low-lying 5Δ state at 1300cm-1 from the 3σ1 1δ1 2π2 configuration. The results of our experimental and theoretical studies will be presented. This work represents the first experimental investigation of the spectra of NbCl and the first ab initio prediction of the spectroscopic properties of the low-lying electronic states. © 2004 Elsevier Inc. All rights reserved.
BibTeX:
@article{Ram2004,
  author = {Ram, R.S. and Rinskopf, N. and Liévin, J. and Bernath, P.F.},
  title = {Fourier transform emission spectroscopy and ab initio calculations on NbCl},
  journal = {Journal of Molecular Spectroscopy},
  year = {2004},
  volume = {228},
  pages = {544-553},
  doi = {10.1016/j.jms.2004.02.001}
}
Abstract: The Auger valence peak of Al2O3, Al and carbon compounds (graphite, fullerene, carbides) has been studied experimentally and theoretically. It is demonstrated, from a comparison of the experimental spectrum with the self-convolution of the valence band, that the Al CVV transition in Al2O3 is an intra-atomic transition. The behaviour of the C KVV Auger peak is shown to be intermediate between atomic and band-like transitions. The different experimental carbide peaks could be reconstructed by a self-convolution of the valence band and the introduction of a hole-hole repulsion term extracted from the Cini-Sawatzki equation. A non-expected behaviour of the satellite peak at 280 eV for tungsten and chromium carbide is shown and interpreted, with a comparison with the Ramaker approach. Copyright © 2004 John Wiley & Sons, Ltd.
BibTeX:
@article{Timmermans2004,
  author = {Timmermans, B. and Hubin, A. and Vaeck, N. and Reniers, F.},
  title = {Experimental and theoretical study of CVV Auger peaks of selected aluminium and carbon compounds},
  journal = {Surface and Interface Analysis},
  year = {2004},
  volume = {36},
  pages = {798-800},
  doi = {10.1002/sia.1767}
}
BibTeX:
@conference{Vaeck2004,
  author = {Vaeck, N. and Godefroid, M.},
  title = {Physica Script T: Preface},
  journal = {Physica Scripta T},
  year = {2004},
  volume = {T112},
  pages = {5},
  doi = {10.1238/Physica.Topical.112a00005}
}
Abstract: The competitive photodissociation of bromoacetyl chloride has been investigated by means of ab initio methods. Quantum dynamics in full dimensionality is prohibitive for such a system and therefore a reduced dimensionality method based on constrained Hamiltonians has been used. A one-dimensional (1-D) non-adiabatic wave packet treatment in the CS optimized geometry (trans Cl and Br) on the first excited states leads to encouraging results when compared to experimental data. The slow relaxation of the torsion angle is assessed by a 2-D dynamics in the subspace including the C=O bond length. © 2003 Elsevier Science B.V. All rights reserved.
BibTeX:
@article{Bacchus-Montabonel2003,
  author = {Bacchus-Montabonel, M.-C. and Vaeck, N. and Lasorne, B. and Desouter-Lecomte, M.},
  title = {Non-adiabatic effects in the photodissociation of bromoacetyl chloride},
  journal = {Chemical Physics Letters},
  year = {2003},
  volume = {374},
  pages = {307-313},
  doi = {10.1016/S0009-2614(03)00606-7}
}
Abstract: A study was performed on the (3 + 1)-resonantly enhanced multiphoton ionization-photoelectron spectroscopy of the (3d-4s) supercomplex of acetylene. The Renner-Teller coupling occurring in the ion ground state was considered during the photoelectron analysis. The results showed the tentative frequencies for the stretching mode as well as for the bending mode.
BibTeX:
@article{Blanchet2003,
  author = {Blanchet, V. and Boyé, S. and Zamith, S. and Campos, A. and Girard, B. and Liévin, J. and Gauyacq, D.},
  title = {(3+1)-resonantly enhanced multiphoton ionization-photoelectron spectroscopy of the (3d-4s) supercomplex of acetylene: The geometry of the E state revisited through experiment and theory},
  journal = {Journal of Chemical Physics},
  year = {2003},
  volume = {119},
  pages = {3751-3762},
  doi = {10.1063/1.1589480}
}
Abstract: This article introduces an alternative perturbation scheme to find approximate solutions of the spectral problem for the rotation-vibration molecular Hamiltonian. The method is implemented for the Watson Hamiltonian and applied to methane. The complete J = 0 spectrum of this penta-atomic molecule of atmospheric interest is calculated up to 9200 cm-1 in a purely ab initio fashion. Then, the rotational spectra of the vibrational ground state is obtained up to J = 18. The largest relative error is 2.10-5 (for the highest J = 18 level) after scaling of a single parameter. Without scaling the accuracy on the rotational levels is limited by that of the ab initio equilibrium bond distance. The convergence of our results is analyzed with respect to the different parameters involved in our approach. The important concept of vibrational mean-field configuration interaction is introduced.
BibTeX:
@article{Cassam-Chenai2003,
  author = {Cassam-Chenaï, P. and Liévin, J.},
  title = {Alternative perturbation method for the molecular vibration-rotation problem},
  journal = {International Journal of Quantum Chemistry},
  year = {2003},
  volume = {93},
  pages = {245-264},
  doi = {10.1002/qua.10556}
}
Abstract: The geometry, ground-state, and optical properties of three isomers of C60Cl24, displaying Th or D2h symmetries were analyzed by means of semiempirical quantum-chemical calculations. Among these, the Th isomer was found to be the preferred thermodynamic product. The results bring some new information on the structure of halogenated fullerenes, which in turn were essential to determine the mechanism of halogen addition onto the carbon cages. Furthermore, the present analysis reinforces the usefulness of the semiempirical calculations of absorption spectra for the determination of the structural and the optical properties of fullerene derivatives.
BibTeX:
@article{Coheur2003,
  author = {Coheur, P.F. and Liévin, J. and Colin, R. and Razbirin, B.},
  title = {Electronic and photophysical properties of C60Cl24},
  journal = {Journal of Chemical Physics},
  year = {2003},
  volume = {118},
  pages = {550-556},
  doi = {10.1063/1.1525807}
}
Abstract: The hyperfine structures of 7,9Be- 2s2p2 4P1/2,3/2,5/2 are investigated theoretically using the multiconfiguration Hartree - Fock and configuration interaction methods. The effects of the hyperfine mixing between the fine-structure J-levels are discussed. The feasibility of some atomic spectroscopy experiments, allowing determination of the 7Be quadrupole moment from the observed hyperfine structure of the 7Be- negative ion and from the present electronic parameters, is investigated. The Be 2s2p 3Po electron affinity is monitored as a function of the orbital and configuration spaces to assess the reliability of the wavefunctions of the neutral atom and the negative ion. The theoretical value nicely converges towards the most recent theoretical and experimental results.
BibTeX:
@article{Nemouchi2003,
  author = {Nemouchi, M. and Jönsson, P. and Pinard, J. and Godefroid, M.},
  title = {Theoretical evaluation of the 7,9Be- 2s2p2 4P1/2,3/2,5/2 hyperfine structure parameters and Be 2s2p 3Po electron affinity},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2003},
  volume = {36},
  pages = {2189-2201},
  doi = {10.1088/0953-4075/36/11/305}
}
Abstract: Hollow atoms are characterized by a large number of vacant inner shells and electrons occupying the outer shells. These 'exotic' atomic species are formed in collision processes between highly-charged ions and several types of targets. The scope of the present contribution is to estimate, using a global approach, the Auger rates of the complex configurations belonging to these atoms.
BibTeX:
@article{Palmeri2003,
  author = {Palmeri, P. and Quinet, P. and Zitane, N. and Vaeck, N.},
  title = {Auger processes in hollow atoms},
  journal = {Revista Mexicana de Fisica},
  year = {2003},
  volume = {49},
  pages = {76-78}
}
Abstract: The emission spectrum of VCl has been investigated at high resolution in the 3000-19 400 cm-1 region using a Fourier transform spectrometer. The bands were excited in a high temperature carbon tube furnace by the reaction of vanadium metal vapor and a trace of BCl3 as well as in a microwave discharge lamp by the reaction of VOCl3 vapor with active nitrogen. The spectra were recorded using the Fourier transform spectrometer associated with the McMath-Pierce telescope of the National Solar Observatory at Kitt Peak. The analysis of the E5 Δ-X5 Δ system of VCl (previously labeled as [7.0]5 Δ-X5Δ) has been extended by analyzing the rotational structure of some additional bands. A rotational analysis of the 5Δ1-5Δ1, 5Δ3-5Δ3, and 5Δ4-5Δ4 subbands of the 0-2, 0-1, 0-0, and 1-0 bands, and the 5Δ2 - 5Δ2 subband of the 0-1 and 0-0 bands has been obtained and molecular constants have been extracted. The 5Δ0± - 5Δ0± subband was not identified in any of the assigned bands. The spectroscopic properties of the low-lying electronic states of VCl have been predicted by CASSCF/CMRCI ab initio calculations and the experimental assignments are supported by the ab initio results.
BibTeX:
@article{Ram2003,
  author = {Ram, R.S. and Liévin, J. and Bernath, P.F. and Davis, S.P.},
  title = {Infrared emission spectroscopy and ab initio calculations on VCl},
  journal = {Journal of Molecular Spectroscopy},
  year = {2003},
  volume = {217},
  pages = {186-194},
  doi = {10.1016/S0022-2852(02)00016-4}
}
Abstract: Cation-π/H-bond stair motifs are recurrently found at the binding interface between protein and DNA. They involve two nucleobases and an amino acid side chain, and encompass three different types of interactions: nucleobase stacking, nucleobase-amino acid H-bond and nucleobase-amino acid cation-π interaction. The interaction energies of the 77 stair motif geometries identified in a data set of 52 high-resolution protein - DNA complexes were investigated by means of ab initio quantum chemistry calculations. Using the standard 6-3IG* basis set, we first establish the value of the Gaussian αd-exponent of d-polarization functions on heavy atoms, which optimizes the MP2 interaction energies. We show that, although the default value of αd = 0.8 is appropriate to minimize the total MP2 energy of a system, the value of αd = 0.2 is optimal for the three types of pairwise interactions studied and yields MP2 interaction energies quite similar to those calculated with more extended basis sets. Indeed, the more diffuse nature of the αd = 0.2 basis functions allows a spatial overlap between the orbitals of the interacting partners. Such functions are also shown to improve the multipole electric moments in the interaction region, which results in a stabilizing polarization effect and a better description of the dispersive energy contributions. Using the MP2 computation level and the 6-31G* basis set with αd = 0.2 instead of αd = 0.8, we computed the interaction energies of the 77 observed stair motif geometries and found that, in a vacuum, the cation-π energy is much less favorable, about 3 times, than the H-bond energy and of the same order of magnitude as the π-π stacking energy. Furthermore, the convergence of the MP perturbation theory expansions was analyzed by computing the MP3 and MP4 corrections on simplified complexes. These expansions exhibited an oscillatory behavior, where MP2 seems to provide a satisfactory approximation, albeit slightly overestimated, to the interaction energy.
BibTeX:
@article{Wintjens2003,
  author = {Wintjens, R. and Biot, C. and Rooman, M. and Liévin, J.},
  title = {Basis set and electron correlation effects on ab initio calculations of cation-π/H-bond stair motifs},
  journal = {Journal of Physical Chemistry A},
  year = {2003},
  volume = {107},
  pages = {6249-6258},
  doi = {10.1021/jp034103q}
}
Abstract: The development of experimental ion-trap techniques provides the opportunity to compare directly theoretical rate coefficients to experimental data in the low-temperature regime. In the present work, we consider the ion-atom collisional systems, N 2+, O 2+, Si 3+ and Si 4+ on a He target, in order to examine the present status of the agreement between theory and experiment.
BibTeX:
@article{Bacchus-Montabonel2002,
  author = {Bacchus-Montabonel, M.-C. and Baloïtcha, E. and Desouter-Lecomte, M. and Vaeck, N.},
  title = {Rate coefficient determination in charge transfer reactions},
  journal = {International Journal of Molecular Sciences},
  year = {2002},
  volume = {3},
  pages = {176-189}
}
Abstract: We report the application of the quantum approach, which takes full account of electron translation at low collisional energies, to the charge exchange process H, D + C 4+ → H +, D + + C 3+(3s; 3p; 3d). The partial and the total integral cross sections of the process are calculated in the energy range from 1 till 60 eV/amu. It is shown that the present results are independent from the upper integration limit for numerical solution of the coupled channel equations although nonadiabatic couplings remain nonzero up to infinity. The calculated partial and total cross sections are in agreement with the previous low-energy calculations and the available experimental data. It is shown that for low collisional energies the isotopic effect takes place. The observed effect is explained in terms of the nonadiabatic dynamics.
BibTeX:
@article{Belyaev2002,
  author = {Belyaev, A.K. and Grosser, J. and Liévin, J. and Vaeck, N.},
  title = {Charge exchange in low-energy H, D + C 4+ collisions with full account of electron translation},
  journal = {International Journal of Molecular Sciences},
  year = {2002},
  volume = {3},
  pages = {190-208}
}
Abstract: The multi-configuration Dirac-Fock model is used to evaluate the magnetic dipole hyperfine interaction constants of the 3d4s(1D)4p 2D3/2,5/20, 3d4s(3D)4p 4F9/20, 3d4s(1D)4p 2F5/2,7/20 and 3d2(1D)4s 2D3/2,5/2 levels of atomic scandium. The wavefunctions are obtained with the active space expansion method, where configuration state functions of a specific parity and J value are generated by substitutions from the reference configurations to an active set of orbitals. The active set is then increased in a systematic way, allowing the convergence of the expectation values to be monitored. The calculated magnetic dipole hyperfine interaction constants are compared with experimentally determined values. On the grounds of the level of agreement between experiment and theory, we confirm three of the hypothetical A-values, previously deduced from high-resolution Fourier transform spectroscopy.
BibTeX:
@article{Bieron2002,
  author = {Bieron, J. and Fischer, C.F. and Godefroid, M.},
  title = {Hyperfine-structure calculations of excited levels in neutral scandium},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2002},
  volume = {35},
  pages = {3337-3345},
  doi = {10.1088/0953-4075/35/15/308}
}
Abstract: Vibrational assignments of fundamental, combination and overtone bands in the main isotopomer of gaseous transformic acid are reported from spectra either newly or previously [J. Chem. Phys. 113 (2000) 1535] recorded using high-resolution Fourier transform and intracavity laser absorption spectroscopies. A total of 62 bands, with 32 newly reported ones, are observed from the lowest energy band, v7 at 626.16 cm-1 up to 4v1 at 13284.1 cm-1. Among these bands, 43 are firmly assigned, and 16 tentatively. Effective vibrational constants are obtained. The normal modes of vibrations are further characterised using ab initio calculations providing fundamental band intensities and picturing normal mode nuclear displacements. The effective investigation of the rotational structure in the first CH stretch overtone band (2v2) and in the second OH stretch overtone band (3v1) is detailed. Rotational information is also presented for 3v2 and two close-lying bands, that could be extracted from the strong overlapping formic acid dimer bands using artificial filtering procedures. © 2002 Elsevier Science B.V. All rights reserved.
BibTeX:
@article{Freytes2002,
  author = {Freytes, M. and Hurtmans, D. and Kassi, S. and Liévin, J. and Vander Auwera, J. and Campargue, A. and Herman, M.},
  title = {Overtone spectroscopy of formic acid},
  journal = {Chemical Physics},
  year = {2002},
  volume = {283},
  pages = {47-61},
  doi = {10.1016/S0301-0104(02)00507-4}
}
Abstract: The theory of CH4-X was generalized for linear molecular perturbers (N2, H2, or CO2). Contributions from the anisotropic quadropolar mechanism were calculated for CH4-N2, CH4-H2, and CH4-CO2. Evidence was obtained that collision-induced absorption arises primarily through the quadrupolar induction mechanism.
BibTeX:
@article{Hartmann2002,
  author = {Hartmann, J.M. and Brodbeck, C. and Flaud, P.-M. and Tipping, R.H. and Brown, A. and Ma, Q. and Liévin, J.},
  title = {Collision-induced absorption in the ν2 fundamental band of CH4. II. Dependence on the perturber gas},
  journal = {Journal of Chemical Physics},
  year = {2002},
  volume = {116},
  pages = {123-127},
  doi = {10.1063/1.1424311}
}
Abstract: The emission spectra of TaN have been investigated in the region 3000-35 000 cm-1 using a Fourier transform spectrometer. The spectra were observed in a tantalum hollow-cathode lamp by discharging a mixture of 1.5 Torr of Ne and about 6 mTorr of N2. In addition to previously known bands, numerous additional bands were observed and assigned to a number of new transitions. The spectroscopic properties of the low-lying electronic states of TaN were also predicted by ab initio calculations. A 1Σ+ state, with equilibrium constants of Be = 0.457 852 1(48) cm-1, αe = 0.002 235 9(67) cm-1, and Re = 1.683 099 9(88) A, has been identified as the ground state of TaN based on our experimental observations supported by the ab initio results. The first excited state has been identified as the a3 Δ1 spin component at 2827 cm-1 above the ground state. To higher energies, the states become difficult to assign because of their Hund’s case (c) behavior and extensive interactions between the spin components of the electronic terms. © 2002 Elsevier Science (USA).
BibTeX:
@article{Ram2002,
  author = {Ram, R.S. and Liévin, J. and Bernath, P.F.},
  title = {Emission spectroscopy and ab initio calculations for TaN},
  journal = {Journal of Molecular Spectroscopy},
  year = {2002},
  volume = {215},
  pages = {275-284},
  doi = {10.1016/S0022-2852(02)98654-6}
}
Abstract: The emission spectra of TaN have been investigated in the region 3000-35 000 cm-1 using a Fourier transform spectrometer. The spectra were observed in a tantalum hollow-cathode lamp by discharging a mixture of 1.5 Torr of Ne and about 6 mTorr of N2. In addition to previously known bands, numerous additional bands were observed and assigned to a number of new transitions. The spectroscopic properties of the low-lying electronic states of TaN were also predicted by ab initio calculations. A 1Σ+ state, with equilibrium constants of Be = 0.457 852 1(48) cm-1, αe = 0.002 235 9(67) cm-1, and Re = 1.683 099 9(88) Å, has been identified as the ground state of TaN based on our experimental observations supported by the ab initio results. The first excited state has been identified as the a3 Δ1 spin component at 2827 cm-1 above the ground state. To higher energies, the states become difficult to assign because of their Hund's case (c) behavior and extensive interactions between the spin components of the electronic terms. © 2002 Elsevier Science (USA).
BibTeX:
@article{Ram2002a,
  author = {Ram, R.S. and Liévin, J. and Bernath, P.F.},
  title = {Emission spectroscopy and ab initio calculations for TaN},
  journal = {Journal of Molecular Spectroscopy},
  year = {2002},
  volume = {215},
  pages = {275-284},
  doi = {10.1006/jmsp.2002.8654}
}
Abstract: Optical spectra of the C60Cl24 halofullerene in the crystalline state, as well as of C60Cl24 matrixisolated molecules, were studied. In both cases, a rich line structure was revealed in absorption spectra in the energy region 1.5-3.0 eV. An energy diagram of the electronic levels of the molecule which are responsible for the observed optical transitions is proposed. The parameters of the geometrical structure of the C60Cl24 molecule were calculated under the assumption of its having Th symmetry. These data were used in a theoretical study of the embedment of the C60Cl24 molecule in a toluene crystal matrix, which leads to the formation of a fine spectral structure (an analog of the Shpol'skii effect) observed experimentally in this study. © 2002 MAIK "Nauka/Interperiodica".
BibTeX:
@article{Razbirin2002,
  author = {Razbirin, B.S. and Starukhin, A.N. and Chugreev, A.V. and Zgoda, A.S. and Smirnov, V.P. and Grushko, Yu.S. and Kolesnik, S.G. and Coheur, P.-F. and Liévin, J. and Colin, R.},
  title = {Absorption line spectrum of the C60Cl24 halofullerene},
  journal = {Physics of the Solid State},
  year = {2002},
  volume = {44},
  pages = {2204-2209},
  doi = {10.1134/1.1521480}
}
Abstract: H-bonds and cation-π interactions between nucleic acid bases and amino acid side-chains are known to occur often concomitantly at the interface between protein and double-stranded DNA. Here we define and analyze stair-shaped motifs, which simultaneously involve base stacking, H-bond and cation-π interactions. They consist of two successive bases along the DNA stack, one in cation-π interaction with an amino acid side-chain that carries a total or partial positive charge, and the other H-bonded with the same side-chain. A survey of 52 high-resolution structures of protein/DNA complexes reveals the occurrence of such motifs in the majority of the complexes, the most frequent of these motifs involving Arg side-chains and G bases. These stair motifs are sometimes part of larger motifs, called multiple stair motifs, which contain several successive stairs; zinc finger proteins for example exhibit up to quadruple stairs. In another kind of stair motif extension, termed cation-π chain motif, an amino acid side-chain or a nucleic acid base forms simultaneously two cation-π interactions. Such a motif is observed in several homeodomains, where it involves a DNA base in cation-π interactions with an Arg in the minor groove and an Asn in the major groove. A different cation-π chain motif contains an Arg in cation-π with a G and a Tyr, and is found in ets transcription factors. Still another chain motif is encountered in proteins that expulse a base from the DNA stack and replace it by an amino acid side-chain carrying a net or partial positive charge, which forms cation-π interactions with the two neighboring bases along the DNA strand. The striking conservation of typical stair and cation-π chain motifs within families of protein/DNA complexes suggests that they might play a structural and/or functional role and might moreover influence electron migration through the DNA double helix. © 2002 Elsevier Science Ltd. All rights reserved.
BibTeX:
@article{Rooman2002,
  author = {Rooman, M. and Liévin, J. and Buisine, E. and Wintjens, R.},
  title = {Cation-π/H-bond stair motifs at protein-DNA interfaces},
  journal = {Journal of Molecular Biology},
  year = {2002},
  volume = {319},
  pages = {67-76},
  doi = {10.1016/S0022-2836(02)00263-2}
}
Abstract: In a talk given in 1986 in honor of Prof. Raymond Daudel, Löwdin famously defined a molecule in the following quantum mechanical terms: "A system of electrons and atomic nuclei is said to form a molecule if the Coulombic Hamiltonian H′ - with the centre of mass motion removed - has a discrete ground state energy E0." We examine this definition in the context of chemical thinking about a molecule and attempt to place it in the context of the developments since the time of that talk. © 2002 Wiley Periodicals, Inc. Int. J. Quantum. Chem.
BibTeX:
@article{Sutcliffe2002a,
  author = {Sutcliffe, B.},
  title = {Some observations on P.-O. Löwdin's definition of a molecule},
  journal = {International Journal of Quantum Chemistry},
  year = {2002},
  volume = {90},
  pages = {66-79},
  doi = {10.1002/qua.1819}
}
Abstract: The quantum dynamics of a system of two polyatomic fragments was studied. The Hamiltonian, designed to describe the quantum dynamics of a nonrigid system comprising two polyatomic molecules in terms of the separation of their centers of mass, was generalized. It was found that the fragments corresponded to a pair of electrons in a diatomic and the angular momentum of the polyatomic fragments played the same role as does the electronic angular momentum in the diatomic case.
BibTeX:
@article{Sutcliffe2002,
  author = {Sutcliffe, B.},
  title = {The quantum dynamics of a system of two polyatomic fragments},
  journal = {Journal of Physical Chemistry A},
  year = {2002},
  volume = {106},
  pages = {10806-10809},
  doi = {10.1021/jp021638v}
}
Abstract: The bonding and electronic structure of surface is most often studied by XPS, where the energy shift of a photoelectron peak can be ascribed to a change in the chemical environment. Because three atomic levels are involved in the Auger emission process, the use of Auger spectroscopy to obtain this information from peak positions and lineshape is more difficult. However, new progress in signal analysis techniques makes the extraction of chemical information intrinsically present in the Auger spectra possible. The advantage of AES over XPS is its higher lateral resolution, allowing study of the surface distribution of the elements (Auger mapping). This, combined with modern computational methods, opens up new opportunities in surface analysis. In order to try to correlate the changes in the Auger peak energies with the changes in the chemical environment, we performed a full experimental and theoretical study of the Auger KLL lines of aluminium in several compounds (Al2O3, AlN, AlB2 and AlF3) by AES and x-ray-induced AES, the peak position for AlB2 being reported for the first time. The inner-shell KLL peaks of Al show large energy shifts, depending on the chemical environment. The experimental results are compared to ab initio calculations based on a new cluster model including chemical, structural and relaxation effects.
BibTeX:
@article{Timmermans2002,
  author = {Timmermans, B. and Vaeck, N. and Hubin, A. and Reniers, F.},
  title = {Chemical effects in Auger electron spectra of aluminium},
  journal = {Surface and Interface Analysis},
  year = {2002},
  volume = {34},
  pages = {356-359},
  doi = {10.1002/sia.1316}
}
Abstract: The statistical properties of a prototype of an atom having a large number of empty inner shells was investigated. The resonance states were found to be strongly overlapping and the number of decay channels was much larger than the number of states. The results showed that the distribution of the nearest-neighbor energy-level spacings followed a Wigner distribution.
BibTeX:
@article{Vaeck2002,
  author = {Vaeck, N. and Kylstra, N.J.},
  title = {Statistical properties of hollow atoms},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2002},
  volume = {65},
  article number = {062502},
  pages = {625021-625028}
}
Abstract: Efficiency of different time-dependent and time-independent wave packet methods for charge-exchange cross sections in ion-atom collisions was discussed. The time-independent spectral projection method, based on the Chebyshev expansion of the resolvent function involved a time propagation while the flux operator method required propagation in time. Flux operator method used the properties of absorbing potentials in order to calculate the flux operator matrix elements.
BibTeX:
@article{Baloitcha2001,
  author = {Baloïtcha, E. and Desouter-Lecomte, M. and Bacchus-Montabonel, M.-C. and Vaeck, N.},
  title = {Wave packet methods for charge exchange processes in ion-atom collisions},
  journal = {Journal of Chemical Physics},
  year = {2001},
  volume = {114},
  pages = {8741-8751},
  doi = {10.1063/1.1367378}
}
Abstract: Measurement of electron affinity of atomic oxygen was done using a photodetachment microscopy. For 17O-, calculation of the hyperfine structure was done, which permitted to add the electron affinity of 17O to the series of the measured electron affinities of oxygen isotopes. Comparison of the anomalous isotope shift of these electron affinities was done with ab initio calculations.
BibTeX:
@article{Blondel2001,
  author = {Blondel, C. and Delsart, C. and Valli, C. and Yiou, S. and Godefroid, M.R. and Van Eck, S.},
  title = {Electron affinities of 16O, 17O, 18O, the fine structure of 16O-, and the hyperfine structure of 17O-},
  journal = {Physical Review A. Atomic, Molecular, and Optical Physics},
  year = {2001},
  volume = {64},
  article number = {052504},
  pages = {525041-5250414}
}
Abstract: The results of ab initio calculations at the MP2 level of theory are presented, which provide refined equilibrium geometrical parameters and better characterization of the vibrational normal modes in propyne (CH3C2H). These results help performing the vibrational analysis of the high resolution Fourier transform absorption spectrum of this molecule which has been recorded between 2000 and 10 200 cm-1. The vibrational assignment criteria also include, in particular, the detailed identification of the band shape based on the observed rotational structure that is resolved for most bands. Some 46 bands are observed and their band shape identified in most cases. Among the bands newly reported, some 14 are vibrationally assigned, three of them tentatively. The relative intensity of all observed bands is estimated from the spectra. Approximate ζ rotational constants are obtained for ν3 + ν6 (0.074) and 2ν1 +ν8 (0.38). The results are merged with those of the previous literature, leading to list the origin of 118 vibrational bands, from which an extensive set of vibrational constants is extracted. Two polyad quantum numbers emerge from the vibrational energy pattern: Nsb = 3v1 + v3 + 2v5 + v9 and Ns = v1 + v3, supported by the ν1 with ν3+ ν5 and ν1 with ν3+ 2ν9 anharmonic resonances. © 2001 Elsevier Science B.V.
BibTeX:
@article{ElIdrissi2001,
  author = {El Idrissi, M.I. and Liévin, J. and Herman, M. and Campargue, A. and Graner, G.},
  title = {The vibrational energy pattern in propyne (12CH312C2H)},
  journal = {Chemical Physics},
  year = {2001},
  volume = {265},
  pages = {273-289},
  doi = {10.1016/S0301-0104(01)00308-1}
}
Abstract: The multiconfiguration Hartree-Fock method is used to calculate wavefunctions in the infinite nuclear mass limit for the terms 2s 2S, 2p 2P o, 3s 2S, 3p 2P o, 3d 2D and 4s 2S of lithium-like ions (3 ≤ Z ≤ 8). Transition data, isotope shift parameters and hyperfine structure electronic contributions involving the six terms of the six ions are evaluated ab initio and compared with the most recent observations and other theoretical calculations when available. The isotopes 7,6Li I, 11,10,9,7Be II, 14,13,12C IV, 15,14N V and 18,17,16 O VI are considered in the analysis of the mass isotope shifts.
BibTeX:
@article{Godefroid2001,
  author = {Godefroid, M. and Froese Fischer, C. and Jönsson, P.},
  title = {Non-relativistic variational calculations of atomic properties in Li-like ions: Li I to O VI},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2001},
  volume = {34},
  pages = {1079-1104},
  doi = {10.1088/0953-4075/34/6/308}
}
Abstract: We have recorded the absorption spectrum of pyrrole (C5H5N) and furan (C4H4O) on a broad spectral range in the infrared region and under various experimental conditions, using a Fourier transform interferometer. The resolution was good enough to reliably identify band shapes. We have performed the vibrational assignment of the vibration-rotation bands observed between 500 and 12,000 cm-1 for pyrrole, and 500 and 9000 cm-1 for furan. The assignment of the fundamental bands is supported by ab initio calculations at the MP2 level of approximation, considering both band positions and absolute absorption intensities. These calculations also allowed the normal mode coordinates to be drawn for the two species and their geometrical structure to be calculated. Vibrational mode numbering and symmetries are updated to latest conventions in the literature. In the combination and overtone spectral ranges, the band shape information guided the assignment, which could be achieved for most of the numerous observed bands. An extensive set of vibration constants was obtained for each species. The results from the literature available on each species are considered at each step of the investigation. © 2001 Elsevier Science B.V. All rights reserved.
BibTeX:
@article{Mellouki2001,
  author = {Mellouki, A. and Liévin, J. and Herman, M.},
  title = {The vibrational spectrum of pyrrole (C4H5N) and furan (C4H4O) in the gas phase},
  journal = {Chemical Physics},
  year = {2001},
  volume = {271},
  pages = {239-266},
  doi = {10.1016/S0301-0104(01)00447-5}
}
Abstract: In this paper, the general behaviour of the Auger rates of hollow atoms for different types of configurations involving identical or non-identical electrons is studied in order to reveal trends in the decay properties of these complex systems. For highly charged ions neutralized with electrons in excited configurations, conventional calculations such as those using available atomic structure codes are generally out of reach. Therefore, we have developed a global approach which allows one to estimate the Auger rates for these 'exotic' systems. When using this method in several simple cases (nitrogen, neon), it has been possible to reproduce level-by-level calculations with good accuracy. Our new approach has allowed us to calculate lifetimes for hollow xenon, lead and thorium ions and the results are discussed in connection with recent experimental data on ion-fullerene collisions.
BibTeX:
@article{Palmeri2001,
  author = {Palmeri, P. and Quinet, P. and Zitane, N. and Vaeck, N.},
  title = {Calculation of Auger rates for complex hollow-atom configurations},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {2001},
  volume = {34},
  pages = {4125-4139},
  doi = {10.1088/0953-4075/34/21/305}
}
Abstract: The proposed electronic assignments of our previously reported near infrared transitions of ZrCl [J. Mol. Spectrosc. 186, 335 (1997); 196, 235 (1999)] have been revised following the suggestion of Sakai, Mogi, and Miyoshi [J. Chem. Phys. 111, 3989 (1999)]. The ground state is now assigned as the X2Δ state followed by the a 4Φ state being the lowest in the quartet manifold. The previously reported transitions [7.3]2Δ-a2Φ, [9.4]2Φ-a2Φ, and C4Δ-X4Φ are now reassigned to C2Φ-X2Δ, E2Φ-X2Δ, and d4Δ-a4Φ, respectively. The new assignments are supported by our own ab initio calculations. Laser excitation spectra of the 414 nm band system have also been observed at low resolution and are attributed to a 4Γ-a4Φ transition. © 2001 American Institute of Physics.
BibTeX:
@article{Ram2001a,
  author = {Ram, R.S. and Adam, A.G. and Sha, W. and Tsouli, A. and Liévin, J. and Bernath, P.F.},
  title = {The electronic structure of ZrCl},
  journal = {Journal of Chemical Physics},
  year = {2001},
  volume = {114},
  pages = {3977-3987}
}
Abstract: The WO molecule was formed as an impurity during the excitation of a mixture of WCl6 vapor and He in a microwave discharge lamp. The emission spectra were recorded using a high-resolution Fourier transform spectrometer. A rotational analysis of the strong bands in the 9000-25000 cm-1 interval has been carried out and the bands have been classified into two groups with different lower states. The two lower states have been assigned as the Ω=0+ and Ω=1 spin components of the X3Σ- ground state. Ab initio calculations have also been performed and they confirm our experimental assignments. © 2001 Elsevier Science B.V.
BibTeX:
@article{Ram2001,
  author = {Ram, R.S. and Liévin, J. and Li, G. and Hirao, T. and Bernath, P.F.},
  title = {The X3Σ- ground state of WO},
  journal = {Chemical Physics Letters},
  year = {2001},
  volume = {343},
  pages = {437-445},
  doi = {10.1016/S0009-2614(01)00704-7}
}
Abstract: When separating the centre of mass motion from the Schrödinger problem for a system, some apparently reasonable choices of space fixed coordinates have transformation properties under nuclear permutations that mix variables that are formally nuclear with those that are formally electronic variables. This renders the idea of a potential surface expressed in such coordinates, problematic. The problems are discussed and some solutions suggested. © 2001.
BibTeX:
@article{Sutcliffe2001,
  author = {Sutcliffe, B.},
  title = {Some mathematical problems in the description of dissociating molecules},
  journal = {Advances in Quantum Chemistry},
  year = {2001},
  volume = {40},
  pages = {17-36}
}
Abstract: The vibrating quadrupole of CH4 interacting with the polarizability of the perturber is proposed as another collision-induced dipole mechanism. This mechanism would be present for absorption in the v2 region. For demonstration purposes, the simplest case of CH4-Ar is considered.
BibTeX:
@article{Tipping2001,
  author = {Tipping, R.H. and Brown, A. and Ma, Q. and Hartmann, J.M. and Boulet, C. and Liévin, J.},
  title = {Collision-induced absorption in the v2 fundamental band of CH4. I. Determination of the quadrupole transition moment},
  journal = {Journal of Chemical Physics},
  year = {2001},
  volume = {115},
  pages = {8852-8857},
  doi = {10.1063/1.1408915}
}
Abstract: The charge exchange Si 4+ + He reaction at low energy and high energy was studied. A time-dependent wave-packet approach was used in low energy range using two different propagator techniques. In high energy range, a semiclassical approach which included Coriolis effects was used. Split-operator technique was used in diabatic representaion and Chebyshev method was used in adiabatic representation for time-dependent approach. Two results were found to be in agreement and thus approved the accuracy of present approach. The order of the magnitude of theoretical values was confirmed by the rate constant of electron transfer reaction calculations.
BibTeX:
@article{Vaeck2001,
  author = {Vaeck, N. and Bacchus-Montabonel, M.-C. and Baloïtcha, E. and Desouter-Lecomte, M.},
  title = {Time-dependent wave-packet treatment of the Si4+ + He collision},
  journal = {Physical Review A. Atomic, Molecular, and Optical Physics},
  year = {2001},
  volume = {63},
  article number = {042704},
  pages = {427041-427048}
}
Abstract: The collisional system Si4++He has been studied over a range of mean relative ion kinetic energy going from 10-2 to 102 eV/amu. In the low-energy range, a time-dependent wave-packet approach is used both in the diabatic and the adiabatic representation using two different propagator techniques. The agreement between the two sets of results assess the accuracy of the present numerical approach. Above 2.5 eV/amu., a semiclassical eikonal calculation is performed, which includes the Coriolis couplings. Finally, the rate constant is calculated and compared with the other theoretical data as well as with the experimental value of [Fang and Kwong, Phys. Rev. A 59, 342 (1999)]. The present results confirm the order of magnitude of previous theoretical values. ©2001 The American Physical Society.
BibTeX:
@article{Vaeck2001a,
  author = {Vaeck, N. and Bacchus-Montabonel, M.-C. and Baloïtcha, E. and Desouter-Lecomte, M.},
  title = {Time-dependent wave-packet treatment of the Si4++He collision},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2001},
  volume = {63},
  article number = {042704},
  pages = {1-8},
  doi = {10.1103/PhysRevA.63.042704}
}
Abstract: Hollow atoms are characterized by a large number of vacant inner shells and electrons occupying the outer shells. These "exotic" atomic species are formed in collision processes between highly-charged ions and several types of targets. The scope of the present contribution is to examine the decay properties of hollow atom states populated in collision with atoms, molecules, solid surfaces and clusters.
BibTeX:
@conference{Vaeck2001b,
  author = {Vaeck, N. and Hansen, J.E. and Palmeri, P. and Quinet, P. and Zitane, N. and Godefroid, M. and Fritzsche, S. and Kylstra, N.},
  title = {Hollow atoms: A theoretical challenge},
  journal = {Physica Scripta T},
  year = {2001},
  volume = {95},
  pages = {68-75}
}
Abstract: In this study, experimental and theoretical values for the oscillator strengths of the 5s2 1S0-5s5p 1,3P10 transitions and for the lifetimes of the 5s5p 1,3P10 levels in the Cd isoelectronic sequence were examined in the context of the evaluation of the importance of core-polarization effects. Erroneous or inaccurate measurements were identified using regularities along the sequence and coherence among the HFR and MCDF results.
BibTeX:
@article{Biemont2000,
  author = {Biémont, E. and Fischer, C.F. and Godefroid, M.R. and Palmeri, P. and Quinet, P.},
  title = {Core-polarization effects in the cadmium isoelectronic sequence},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {2000},
  volume = {62},
  pages = {032512-032511}
}
Abstract: The photophysical properties of hexa-functionalized C60 derivatives (C60Cl6, C60Ph5Cl, C60Ph5H, and two C60Ph5OH isomers) have been investigated by means of UV-visible absorption and fluorescence spectroscopy in cyclohexane solution and quantum-chemical calculations derived from semiempirical Hartree-Fock approaches. A very good agreement is obtained between the measured absorption and fluorescence spectra and the calculated excitation energies, thus allowing for a detailed assignment of the optical features. The effects of symmetry and chemical nature of the functional groups on the ground-state and spectroscopic properties of the C60 derivatives are discussed. © 2000 American Institute of Physics.
BibTeX:
@article{Coheur2000,
  author = {Coheur, P.-F. and Cornil, J. and Dos Santos, D.A. and Birkett, P.R. and Liévin, J. and Brédas, J.L. and Walton, D.R.M. and Taylor, R. and Kroto, H.W. and Colin, R.},
  title = {Photophysical properties of hexa-functionalized C60 derivatives: Spectroscopic and quantum-chemical investigations},
  journal = {Journal of Chemical Physics},
  year = {2000},
  volume = {112},
  pages = {8555-8566}
}
Abstract: The photophysics of six multiply phenylated C70 derivatives [C70Ph2, C70Ph4, C70Ph6 (two regioisomers), C70Ph8 and C70Ph10] have been investigated by means of steady state spectroscopy in cyclohexane solution and quantum-chemical calculations derived from semiempirical Hartree-Fock approaches. There is good agreement between the measured absorption spectra and the INDO/SCI calculated excitation energies for each derivative. The foregoing results and some additional ground state properties calculated at the AMI level have been used to predict that the perturbation of the π electronic system of the cage results in significant changes in the photophysics of the fullerene derivatives. The effects of conjugation and spatial localization of the HOMO and LUMO orbitals on the energy of the first electronic transition are discussed in greater detail. © 2000 American Institute of Physics.
BibTeX:
@article{Coheur2000a,
  author = {Coheur, P.-F. and Cornil, J. and Dos Santos, D.A. and Birkett, P.R. and Liévin, J. and Brédas, J.L. and Walton, D.R.M. and Taylor, R. and Kroto, H.W. and Colin, R.},
  title = {Photophysical properties of multiply phenylated C70 derivatives: Spectroscopic and quantum-chemical investigations},
  journal = {Journal of Chemical Physics},
  year = {2000},
  volume = {112},
  pages = {6371-6381}
}
Abstract: Transition probabilities of the radiative decay processes of the excited levels 2p4(3P)3d 4D7/2, 2F7/2 and 4F7/2 of the fluorine-like neon ion (Ne+) are evaluated by variational calculations using superposition of configurations in the Breit-Pauli approximation. The strong 2F7/2-4F7/2 relativistic mixing is discussed in terms of level designation and doublet-quartet intensity transfer. A detailed comparison of the results with other theories and with the NIST measurements of branching fractions, combined with lifetime measurements, confirms problems on the experimental side.
BibTeX:
@article{Godefroid2000,
  author = {Godefroid, M.R. and Hibbert, A.},
  title = {Theoretical lifetimes and branching fractions of 2p4(3P)3d 4D7/2, 2F7/2 and 4F7/2 in Ne II},
  journal = {Molecular Physics},
  year = {2000},
  volume = {98},
  pages = {1099-1106},
  doi = {10.1080/00268970050080465}
}
Abstract: In this study, three different inputs dedicated to the OH bond excitation in trans-formic acid were merged. First, experiments were carried out using FTS. Following this, ICLAS was used to record the 4vOH band at high spectral region. Finally, ab initio calculations were performed. Overall, the results indicate the occurrence of a chemical mechanism different from those usually probed with overtone spectroscopy.
BibTeX:
@article{Hurtmans2000,
  author = {Hurtmans, D. and Herregodts, F. and Herman, M. and Liévin, J. and Campargue, A. and Garnache, A. and Kachanov, A.A.},
  title = {Spectroscopic and ab initio investigation of the vOH overtone excitation in trans-formic acid},
  journal = {Journal of Chemical Physics},
  year = {2000},
  volume = {113},
  pages = {1535-1545},
  doi = {10.1063/1.481939}
}
Abstract: Multiconfiguration Hartree-Fock (MCHF) and configuration interaction (CI) calculations have been performed for the low-lying levels 2p4 3P, 2p3(4S0)3s 3,5S0 and 2p3(4S0)3p 3,5P0 of neutral oxygen. Different cancellation effects on the specific mass shift, on the electronic contributions to hyperfine interaction constants and on the length and velocity forms of oscillator strengths are illustrated. The final CI values are compared with experimental values and, when available, with values from other theories.
BibTeX:
@article{Joensson2000,
  author = {Jönsson, P. and Godefroid, M.R.},
  title = {Theoretical studies of isotope shifts, hyperfine structures and oscillator strengths in transitions between low-lying levels in O I},
  journal = {Molecular Physics},
  year = {2000},
  volume = {98},
  pages = {1141-1149},
  doi = {10.1080/00268970050080500}
}
Abstract: The emission spectrum of HfCl has been investigated in the 3000-18 500 cm-1 region at high resolution using a Fourier transform spectrometer. The bands were excited in a microwave discharge through a flowing mixture of HfCl4 and helium. Two bands near 17 140 and 17 490 cm-1 were also measured in absorption using laser excitation spectroscopy. In this instance the molecules were created by laser ablation in a molecular beam apparatus. The observed bands have been classified into two electronic transitions, [7.6]4Δ3/2-X2Δ3/2 and [17.1]2Δ3/2-X2Δ3/2 involving a common lower state. A rotational analysis of the 0-0 and 1-1 bands of [7.6]4Δ3/2-X2Δ3/2 and 0-0, 1-1, and 1-0 bands of the [17.1]2Δ3/2-X2Δ3/2 transitions has been carried out and the equilibrium spectroscopic constants have been determined. The ground state principal molecular constants are Be = 0.1097404(54) cm-1, αe = 0.0004101(54) cm-1, and re = 2.290532(57) angstrom. Ab initio calculations have been performed on HfCl and spectroscopic properties of the low-lying electronic states have been predicted. The ground state is predicted to be a regular 2Δ state arising from the valence electron configuration, 1σ22σ23σ21π41δ1. On the basis of our ab initio calculations, we assign the observed transitions as [7.6]4Δ3/2-X2Δ3/2 and [17.1]2Δ3/2-X2Δ3/2.
BibTeX:
@article{Ram2000,
  author = {Ram, R.S. and Adam, A.G. and Tsouli, A. and Liévin, J. and Bernath, P.F.},
  title = {High-resolution spectroscopy and Ab initio calculations on HfCl},
  journal = {Journal of molecular spectroscopy},
  year = {2000},
  volume = {202},
  pages = {116-130},
  doi = {10.1006/jmsp.2000.8120}
}
BibTeX:
@article{Sutcliffe2000,
  author = {Sutcliffe, B.},
  title = {The decoupling of electronic and nuclear motions in the isolated molecule SchröDinger Hamiltonian},
  journal = {Advances in Chemical Physics},
  year = {2000},
  volume = {114},
  pages = {118-121}
}
Abstract: Cation-π interactions between an aromatic ring and a positive charge located above it have proven to be important in protein structures and biomolecule associations. Here, the role of these interactions at the interface of protein-DNA complexes is investigated, by means of ab initio quantum mechanics energy calculations and X-ray structure analyses. Ab initio energy calculations indicate that Na ions and DNA bases can form stable cation-π complexes, whose binding strength strongly depends on the type of base, on the position of the Na ion, and whether the base is isolated or included in a double-stranded B-DNA. A survey of protein-DNA complex structures using appropriate geometrical criteria revealed cation-π interactions in 71% of the complexes. More than half of the cation-π pairs involve arginine residues, about one-third asparagine or glutamine residues that only carry a partial charge, and one-seventh lysine residues. The most frequently observed pair, which is also the most stable as monitored by ab initio energy calculations, is arginine-guanine. Arginine-adenine interactions are also favorable in general, although to a lesser extent, whereas those with thymine and cytosine are not. Our calculations show that the major contribution to cation-π interactions with DNA bases is of electrostatic nature. These interactions often occur concomitantly with hydrogen bonds with adjacent bases; their strength is estimated to be from three to four times lower than that of hydrogen bonds. Finally, the role of cation-π interactions in the stability and specificity of protein-DNA complexes is discussed. (C) 2000 Academic Press.
BibTeX:
@article{Wintjens2000,
  author = {Wintjens, R. and Liévin, J. and Rooman, M. and Buisine, E.},
  title = {Contribution of cation-π interactions to the stability of protein-DNA complexes},
  journal = {Journal of Molecular Biology},
  year = {2000},
  volume = {302},
  pages = {395-410}
}
Abstract: We report on the projectile energy dependence of the cross sections for producing K Auger electrons in 2-170-keV N7++Ne collisions. The present studies, which extend previous work performed at the impact energy of 35 keV, give evidence for a dielectronic excitation process produced by electron-electron interaction. At impact energies in the range 5-170 keV, the cross sections are found to be larger than 10-17 cm2. Molecular-orbital energy diagrams were determined to analyze details of the collision. Analytic models were used to evaluate cross sections associated with dielectronic excitation. The results show good agreement with experiment. The dielectronic excitation process is dominant when three electrons from the target are transferred into an excited state of the projectile. ©1999 The American Physical Society.
BibTeX:
@article{Bedouet1999,
  author = {Bedouet, C. and Frémont, F. and Chesnel, J.Y. and Husson, X. and Merabet, H. and Vaeck, N. and Zitane, N. and Sulik, B. and Grether, M. and Spieler, A. and Stolterfoht, N.},
  title = {Dielectronic excitation of Ne K-shell electrons in 2-170-keV N7++Ne collisions},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {1999},
  volume = {59},
  pages = {4399-4406}
}
Abstract: The geometry and electronic structure of three C60 derivatives (C60Cl6, C60Ph5Cl and C60Ph5H) are studied by means of spectroscopic measurements in cyclohexane solution and semi-empirical Hartree-Fock quantum-chemical calculations. A good agreement between observed and simulated spectra is reported. Based on the latter, the importance of symmetry and nature of the functional groups on the properties of the C60 cages is discussed.
BibTeX:
@article{Coheur1999,
  author = {Coheur, P.-F. and Cornil, J. and Dos Santos, D.A. and Birkett, P.R. and Liévin, J. and Brédas, J.L. and Janot, J.-M. and Seta, P. and Leach, S. and Walton, D.R.M. and Taylor, R. and Kroto, H.W. and Colin, R.},
  title = {Photophysical properties of C60Cl6, C60Ph5Cl and C60Ph5H},
  journal = {Synthetic Metals},
  year = {1999},
  volume = {103},
  pages = {2407-2410},
  doi = {10.1016/S0379-6779(98)00250-1}
}
Abstract: A total of 134 vibrational levels with assigned rotational structure have been gathered in the ground electronic state of 13C2H2. Most of these measurements are updated or new compared to the previously published data. Altogether, they cover the range up to 23 670 cm-1. 118 out of the 119 levels observed below 13 000 cm-1 have been simultaneously fitted using the so-called cluster model, already used to deal with the vibrational energy levels in other isotopomers of acetylene [El Idrissi et al., J. Chem. Phys. 110, 2074 (1999), and references therein]. Twenty-nine vibrational constants have been determined, including the off-diagonal parameters K3/245, K1/244, K1/255, K11/33, K14/35, and r45, with a rms of the fit equal to 0.52 cm-1. The same three constants of the motion as in 12C2H2 emerged, Ns = v1+v2+v3, Nr=5v1+3v2+5v3+v4+v 5 and k=l4+l5. The energies of the levels above 13 000 cm-1 calculated with the obtained parameters compare reasonably well with the experimental values. For all levels the predicted rotational constants compare satisfactorily with the experimental results. © 1999 American Institute of Physics.
BibTeX:
@article{DiLonardo1999,
  author = {Di Lonardo, G. and Fusina, L. and Venuti, E. and Johns, J.W.C. and El Idrissi, M.I. and Liévin, J. and Herman, M.},
  title = {The vibrational energy pattern in acetylene. V. 13C2H2},
  journal = {Journal of Chemical Physics},
  year = {1999},
  volume = {111},
  pages = {1008-1016}
}
Abstract: All 253 vibrational levels in the ground electronic state of 12C2H2 with assigned rotational structure reported in the literature from absorption, stimulated emission pumping, and dispersed laser induced fluorescence spectroscopic investigations are gathered. They cover the range up to 18915 cm-1. Some 219 of these energies are simultaneously fitted using the same so-called Cluster model based on the emergence of three constants of the motion, as previously used to deal with the vibrational energy levels up to 12 000 cm-1 [Abbouti Temsamani and Herman, J. Chem. Phys. 103, 5931 (1995)]. Thirty-nine vibrational constants are produced. The rms value of the fit is 0.81 cm-1. Principal rotational constants are predicted for all levels, which satisfactorily compare with the experimental results. Problems are demonstrated to concern a fraction of the 34 remaining levels only. Thus, the adequacy of the model is fully confirmed. The remaining problems are discussed and globally attributed to problems of a vibration-rotation nature. A comprehensive listing of calculated vibrational energies for all k sublevels up to 15 000 cm-1, including predicted Bv, values and assignments is made available. © 1999 American Institute of Physics.
BibTeX:
@article{ElIdrissi1999,
  author = {El Idrissi, M.I. and Liévin, J. and Campargue, A. and Herman, M.},
  title = {The vibrational energy pattern in acetylene (IV): Updated global vibration constants for 12C2H2},
  journal = {Journal of Chemical Physics},
  year = {1999},
  volume = {110},
  pages = {2074-2086}
}
Abstract: Recent years have seen a growing number of large-scale atomic structure calculations using both nonrelativistic and relativistic theories. For investigations of multiple and highly charged ions, of course, a relativistic structure code like the widely known GRASP program is required. In a revised version of this program, namely GRASP92 [F.A. Parpia, C.F. Fischer, and I.P. Grant, Comput. Phys. Commun. 94, 249 (1996)], systematic studies of level energies and a few other bound-state properties are now being supported. - Here, we briefly introduce a new package RATIP which extends GRASP92 towards the computation of various Relativistic AtomicTransition and Ionization Properties. A short overview of the capabilities of RATIP along with current developments will be given.
BibTeX:
@conference{Fritzsche1999,
  author = {Fritzsche, S. and Koike, F. and Sienkiewicz, J.E. and Vaeck, N.},
  title = {Calculation of relativistic atomic transition and ionization properties for highly-charged ions},
  journal = {Physica Scripta T},
  year = {1999},
  volume = {80},
  pages = {479-481}
}
Abstract: The present paper reports the ab initio evaluation of the electron affinity of oxygen, and the value of its isotope shift. The theoretical results are in good agreement with the recent electron affinity measurements for 16O and 18O by photodetachment microscopy, revealing an "anomalous" isotope shift. The theoretical fine structure of the negative ion 2p5 2Po1/2-3/2 is also in very good agreement with observation.
BibTeX:
@article{Godefroid1999,
  author = {Godefroid, M.R. and Fischer, C.F.},
  title = {Isotope shift in the oxygen electron affinity},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {1999},
  volume = {60},
  pages = {R2637-R2640}
}
Abstract: The oscillator strengths of the Mg+ weak transitions 3s 2S1/2-4p 2P3/2, 1/2o at λ = 1239, 1240 angstrom are evaluated using the multiconfiguration Hartree-Fock approach combined with the orbital active set method and configuration-interaction calculations, taking the effect of triple and quadruple excitations into account. The effects of core and core-valence correlation using different optimization schemes are discussed in detail. Relativistic corrections are calculated within the Breit-Pauli approximation.
BibTeX:
@article{Godefroid1999a,
  author = {Godefroid, M. and Froese Fischer, C.},
  title = {Mg+ 3s 2S1/2-4p 2P3/2, 1/2o weak transition probabilities revisited},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1999},
  volume = {32},
  pages = {4467-4483},
  doi = {10.1088/0953-4075/32/18/307}
}
BibTeX:
@article{Herman1999,
  author = {Herman, M. and Lievin, J. and Vander Auwera, J. and Campargue, A.},
  title = {Global and accurate vibration Hamiltonians from high-resolution molecular spectroscopy},
  journal = {Advances in Chemical Physics},
  year = {1999},
  volume = {108},
  pages = {1-330}
}
Abstract: Results from systematic multiconfiguration Hartree-Fock calculations of isotope shifts and oscillator strengths are reported for the 2s2 - 2s2p and 2s2p - 2p2 transitions in the Be isoelectronic sequence (Z = 4-10). In addition values for the same properties as well as for the hyperfine interaction constants are presented for the 3s2-3s3p transitions in Mg I. Different models for electron correlation are used, and it is shown that valence and core-valence effects alone are not sufficient to obtain accurate values for the isotope shifts, but that also core-core effects need to be accounted for.
BibTeX:
@article{Joensson1999,
  author = {Jönsson, P. and Froese Fischer, C. and Godefroid, M.R.},
  title = {MCHF calculations of isotope shifts and oscillator strengths for transitions between low-lying states in Be-like systems and neutral magnesium},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1999},
  volume = {32},
  pages = {1233-1245},
  doi = {10.1088/0953-4075/32/5/015}
}
Abstract: The emission spectrum of IrN was recorded in the near infrared using a Fourier transform spectrometer. The IrN molecules were excited in an Ir hollow cathode lamp operated with a mixture of Ne and a trace of N2. Numerous IrN bands observed in the 7500-9200 cm-1 region were assigned to a new a3Π-X1Σ+ electronic transition with the 0-0 bands of the a3Π0-X1Σ+ and a3Π1-X1Σ+ subbands near 9175 and 8841 cm-1, respectively. A rotational analysis of several bands of the 0-0 and 0-1 sequences was obtained and molecular constants were extracted. The effective Hund's case (a) constants for the new a3Π state are: T00 = 8840.31747(88) cm-1, A0 = -340.53329(93) cm-1, ΔG(1/2) = 984.3629(23) cm-1, Be = 0.4699116(27) cm-1, αe = 0.0030058(50) cm-1, and re= 1.6576432(47) Å. The spectroscopic properties of the ground state and several low-lying electronic states of IrN were also predicted by ab initio calculations. These calculations are consistent with our assignment of the a3Π-X1Σ+ transition and also support our previous assignments of the A′ 1Π and A1Π electronic states [R. S. Ram and P. F. Bernath, J. Mol. Spectrosc. 193, 363 (1999)]. The excited a3Π state of IrN has an 1σ22σ21π43σ 11δ4π1 electron configuration and the configurations of the other low-lying electronic states are also discussed. © 1999 Academic Press.
BibTeX:
@article{Ram1999a,
  author = {Ram, R.S. and Liévin, J. and Bernath, P.F.},
  title = {Emission Spectroscopy and Ab Initio Calculations on IrN},
  journal = {Journal of Molecular Spectroscopy},
  year = {1999},
  volume = {197},
  pages = {133-146},
  doi = {10.1006/jmsp.1999.7911}
}
Abstract: The emission spectrum of OsN has been recorded in the 3000-13000 cm-1 region using a Fourier transform spectrometer. OsN molecules were excited in an osmium hollow cathode lamp operated with neon gas and a trace of nitrogen. Six bands observed in the 8000-12 200 cm-1 region have been classified into three transitions, a 4Π5/2-X2Δ5/2, b 4Φ5/2-X2Δ5/2, and b 4Φ5/2-X2Δ5/2 with the 0-0 band origins near 8381.7, 11 147.9, and 12 127.2 cm-1, respectively. A rotational analysis of these bands provides the following equilibrium constants for the ground electronic state: ωe = 1147.9492(77) cm-1, ωexe=5.4603(36) cm-1, Be=0.493 381(55) cm-1, αe = 0.002753(38) cm-1, and re = 1.618 023(91) Å. Ab initio calculations have been performed on OsN and the spectroscopic properties of the low-lying electronic states have been calculated. Our assignments are supported by these calculations. The ground state of OsN has been identified as a 2Δi state consistent with the observations for the isoelectronic IrC molecule [Jansson et al., Chem. Phys. Lett. 4, 188 (1969); J. Mol. Spectrosc. 36, 248 (1970)]. The 1σ22σ21π41δ 3σ2 electron configuration has been proposed for the ground state and the configurations for the other low-lying electronic states have also been discussed. This work represents the first experimental or theoretical investigation of the electronic spectra of OsN. © 1999 American Institute of Physics.
BibTeX:
@article{Ram1999,
  author = {Ram, R.S. and Liévin, J. and Bernath, P.F.},
  title = {Fourier transform emission spectroscopy and ab initio calculations on OsN},
  journal = {Journal of Chemical Physics},
  year = {1999},
  volume = {111},
  pages = {3449-3456}
}
Abstract: Modern nonempirical calculations of the rotation-vibration spectra of small molecules often use a dipole moment surface computed from a clamped nuclei electronic structure calculation to determine the transition intensities. In this article, an attempt is made to analyze what exactly is involved in such an enterprise. © 1999 John Wiley & Sons, Inc. Int J Quant Chem 74: 681-695, 1999.
BibTeX:
@article{Sutcliffe1999a,
  author = {Sutcliffe, B.T.},
  title = {Dipole moment surfaces and spectroscopic calculations},
  journal = {International Journal of Quantum Chemistry},
  year = {1999},
  volume = {74},
  pages = {681-695}
}
Abstract: An attempt is made to formulate the Born-Oppenheimer correction terms arising from the interaction of the electronic and nuclear motions in a triatomic system. The formulation for the nuclear motion problem is kept as general as possible while using the nuclei to define the instantaneous (x-z) plane, following the approach presented in Sutcliffe and Tennyson. © 1999 John Wiley & Sons, Inc.
BibTeX:
@article{Sutcliffe1999,
  author = {Sutcliffe, B.T.},
  title = {The born-oppenheimer correction terms for a triatomic system in the sutcliffe-tennyson formulation},
  journal = {International Journal of Quantum Chemistry},
  year = {1999},
  volume = {74},
  pages = {109-121}
}
Abstract: The collisional system C4+ + H is studied as a test case to assess the efficiency of a full quantum time-dependent method to calculate charge-exchange cross sections. The molecular diabatic electronic channels are calculated at the CASSCF level from the adiabatic potential energy curves and the radial coupling matrix. The elements of the collision matrix are extracted, for each value of the total angular momentum K, by Fourier transforming the post-collisional amplitudes of the wavepackets which are prepared in the entry channel C4+ + H and propagated on the coupled effective channels for each value of K. The results are compared with previous calculations of cross sections obtained by solving the stationary scattering equations and with recent experimental results. The close-coupling wavepacket method also provides a time-dependent picture of the collision dynamics for any K value. The kinematic isotopic effect is also examined.
BibTeX:
@article{Vaeck1999,
  author = {Vaeck, N. and Desouter-Lecomte, M. and Liévin, J.},
  title = {Non-adiabatic wavepacket dynamics for charge-exchange processes in ion-atom collisions: Application to C4+ + H},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1999},
  volume = {32},
  pages = {409-428},
  doi = {10.1088/0953-4075/32/2/021}
}
Abstract: The J = 0 → J′ = 0 radiative transitions, usually viewed as allowed through two-photon decay, may also be induced by the hyperfine (HPF) interaction in atoms or ions having a nonzero nuclear spin. We compute new and review existing decay rates for the nsnp 3PJo → ns2 1SJ′ = 0 transitions in ions of the Be (n = 2) and Mg (n = 3) isoelectronic sequences. The HPF induced decay rates for the J = 0 → J′ = 0 transitions are many orders of magnitude larger than those for the competing two-photon processes, and when present are typically 1 or 2 orders of magnitude smaller than the decay rates of the magnetic quadrupole (J = 2 → J′ = 0) transitions for these ions. Several HPF induced transitions are potentially of astrophysical interest in ions of C, N, Na, Mg, Al, Si, K, Cr, Fe, and Ni. We highlight those cases that may be of particular diagnostic value for determining isotopic abundance ratios and/or electron densities from UV or EUV emission-line data. We present our atomic data in the form of scaling laws so that, given the isotopic nuclear spin and magnetic moment, a simple expression yields estimates for HPF induced decay rates. We examine some UV and EUV solar and nebular data in light of these new results and suggest possible applications for future study. We could not find evidence for the existence of HPF induced lines in the spectra we examined, but we demonstrate that existing data have come close to providing interesting upper limits. For the planetary nebula SMC N2, we derive an upper limit of 0.1 for 13C/12C from Goddard High-Resolution Spectrograph data obtained by Clegg. It is likely that more stringent limits could be obtained using newer data with higher sensitivities in a variety of objects. © 1998. The American Astronomical Society. All rights reserved.
BibTeX:
@article{Brage1998,
  author = {Brage, T. and Judge, P.G. and Aboussaïd, A. and Godefroid, M.R. and Jönsson, P. and Ynnerman, A. and Fischer, C.F. and Leckrone, D.S.},
  title = {Hyperfine induced transitions as diagnostics of isotopic composition and densities of low-density plasmas},
  journal = {Astrophysical Journal},
  year = {1998},
  volume = {500},
  pages = {507-521},
  doi = {10.1086/305690}
}
BibTeX:
@article{Doggett1998,
  author = {Doggett, G. and Sutcliffe, B.},
  title = {A modern approach to L-S coupling in the theory of atomic spectra},
  journal = {Journal of Chemical Education},
  year = {1998},
  volume = {75},
  pages = {110-114}
}
Abstract: Some properties of atoms defined in terms of two-electron operators are investigated for sodium. Systematic multiconfiguration Hartree-Fock (MCHF) methods are used. Of particular interest are the energy, the isotope shift parameter, and a dipole-dipole parameter defined as the expectation value of the operator (∑iri)2. Unlike the one-electron dipole operator, where the line strength was predicted accurately from single, double, and triple excitations, these properties require that quadruple excitations also be considered.
BibTeX:
@article{Fischer1998a,
  author = {Fischer, C.F. and Jönsson, P. and Godefroid, M.},
  title = {Some two-electron properties of sodium},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {1998},
  volume = {57},
  pages = {1753-1758}
}
Abstract: Multiconfiguration Breit-Pauli energy levels, lifetimes, and transition data are presented for the lithium sequence in the rangeZ≤ 8. Included are allJ-levels of the six lowest2Lterms, namely those with configuration labels 1s22s, 1s22p, 1s23s, 1s23p, 1s23d, and 1s24s. © 1998 Academic Press.
BibTeX:
@article{Fischer1998,
  author = {Fischer, C.F. and Saparov, M. and Gaigalas, G. and Godefroid, M.},
  title = {Breit-pauli energies, transition probabilities, and lifetimes for 2s, 2p, 3s, 3p, 3d, 4s2llevels of the lithium sequence,Z= 3-8},
  journal = {Atomic Data and Nuclear Data Tables},
  year = {1998},
  volume = {70},
  pages = {119-134},
  doi = {10.1006/adnd.1998.0788}
}
Abstract: The superposition of configurations (SOC) method has been used to calculate f-values for the Mg H doublet at 1240 Å, which has been observed in the interstellar medium near stars such as ζ Ophiuchi. Our best value for the multiplet oscillator strength is 0.00083. SOC calculations have also been undertaken for the stronger (3s-3p) doublet at 2800 Å giving a multiplet f-value of 0.92.
BibTeX:
@article{Fleming1998,
  author = {Fleming, J. and Hibbert, A. and Bell, K.L. and Vaeck, N.},
  title = {The 3s 2S-4p 2Po transition probability in Mg II},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {1998},
  volume = {300},
  pages = {767-772}
}
Abstract: Recent ab initio variational calculations of radiative transition probabilities, isotope shifts and hyperfine structures are described in the spirit of the EGAS tradition for plenary talks. A few simple cases are selected to make the exposé at a level accessible to non-specialists in the field and to illustrate how computational atomic structure can be used in atomic spectroscopy for testing theoretical models or experimental results, predicting properties or interpreting them in terms of electron correlation. The effects inherent in the multiconfiguration Hartree-Fock method due to its variational nature are emphasized through some simple analysis of the wave function spatial distribution in correlation with the model used. © Physica Scripta 1998.
BibTeX:
@conference{Godefroid1998,
  author = {Godefroid, M.R. and Jönsson, P. and Fischer, C.F.},
  title = {Atomic structure variational calculations in spectroscopy},
  journal = {Physica Scripta T},
  year = {1998},
  volume = {78},
  pages = {33-46}
}
Abstract: The potential energy surfaces of the three low lying electronic states of NO2, namely the X̃ 2A1, Ã 2B2, and B̃ 2B1 states, and the transition dipole moment surfaces between the ground state and both excited states have been calculated at two levels of ab initio theory; complete active space self-consistent field (CASSCF) and internally contracted multireference configuration interaction (CMRCI). Only 9 points of these surfaces, located around the equilibrium geometry of X̃ 2A1 and corresponding to C2v geometries, have been found sufficient for calculating the cross section, in the 10000-45000 cm-1 energy range, by means of a 2D version of the reflection method. The agreement between the experimental low resolution data and the ab initio absorption cross section is satisfactory, mainly at the CMRCI level, at which the energy at maximum amplitude, the width, the maximum amplitude and the effective transition dipole moment describing both involved electronic transitions are predicted within 4%, 6%, 20%, and 11%, respectively. The sources of errors coming from the reflection approximation and from the level of ab initio approximation are analyzed on the basis of test calculations. The relative importance of the different contributions to the total cross section (both electronic transitions, cold and hot bands) is also discussed. In addition, quantum calculations based on Franck-Condon factors have been performed in order to improve the description of the low energy part of the cross section and to interpret the observed radiative lifetimes. © 1998 American Institute of Physics.
BibTeX:
@article{Lievin1998,
  author = {Liévin, J. and Delon, A. and Jost, R.},
  title = {Absorption cross section of NO2 by the reflection method from ab initio calculations involving the three low lying electronic states},
  journal = {Journal of Chemical Physics},
  year = {1998},
  volume = {108},
  pages = {8931-8943}
}
Abstract: The emission spectrum of RuN has been observed in the near infrared using a Fourier transform spectrometer. RuN molecules were excited in a hollow cathode lamp operated with neon gas and a trace of nitrogen. Two bands with 0-0 Q heads near 7354 and 8079 cm-1 and a common lower state have been assigned as 2Π1/2-2Σ+ and 2Π3/2-2Σ+ subbands, respectively, of a C2Π-X2Σ+ transition. A rotational analysis of these bands has been performed and molecular constants have been extracted. The principal molecular constants for the ground X2Σ+ state of the most abundant 102RuN isotopomer are: B0=0.5527829(70)cm-1, D0=5.515(13)×10-7cm-1, γ0 =-0.044432(22)cm-1 and r0=1.573869(10)Å. The excited C2Π state has the following molecular constants: T00=7714.34260(53)cm-1, A0=725.8064(11)cm-1, B0=0.5168434(80)cm-1, D0=5.685(16)×10-7cm-1, p0=5.467(36)×10-3cm-1 and r0=1.627670(13)Å. Ab initio calculations have been carried out on RuN to ascertain the nature of the experimentally observed states and to predict the spectroscopic properties of the low-lying electronic states. Our electronic assignment is supported by these calculations and is also consistent with the observations for the isoelectronic RhC molecule [Kaving and Scullman, J. Mol. Spectrosc. 32, 475-500 (1969)]. The valence electron configuration 1σ22σ21π41δ 43σ1 is proposed for the X2Σ+ ground state of RuN and the configurations for the excited states have been discussed. There is no previous experimental or theoretical work on RuN. © 1998 American Institute of Physics.
BibTeX:
@article{Ram1998,
  author = {Ram, R.S. and Liévin, J. and Bernath, P.F.},
  title = {Fourier transform infrared emission spectroscopy and ab initio calculations on RuN},
  journal = {Journal of Chemical Physics},
  year = {1998},
  volume = {109},
  pages = {6329-6337},
  doi = {10.1063/1.477275}
}
Abstract: The topics to be discussed at this meeting are surveyed in an attempt to place them in the context of the considerations of our last meeting and of developments since then. © 1999 Academic Press Inc.
BibTeX:
@article{Sutcliffe1998,
  author = {Sutcliffe, B.T.},
  title = {Quantum Systems in Chemistry and Physics: Some Hopes and Fears},
  journal = {Advances in Quantum Chemistry},
  year = {1998},
  volume = {31},
  pages = {1-13},
  doi = {10.1016/S0065-3276(08)60180-X}
}
Abstract: The trans and gauche isomers of 1,-dichloroethane are characterized using ab initio calculations at the MP4(SDQ) level of theory with the full double zeta polarized D95** basis set. The molecular geometry parameters, the torsion potential and the harmonic frequency of the normal modes of vibrations are calculated. The integrated intensity and the rotational type of the infrared fundamental bands also are determined. New labelling of the normal modes of vibration is introduced for the gauche isomer. The relative abundance and stability of both isomers are discussed. The torsional motion is investigated by means of an effective model taking the geometrical relaxation into account and leading to a theoretical torsional spectrum. © 1998 Taylor & Francis Group, LLC.
BibTeX:
@article{Youssoufi1998,
  author = {Youssoufi, Y.E. and Herman, M. and Lievin, J.},
  title = {The ground electronic state of 1,-dichloroethane I. Ab initio investigation of the geometrical, vibrational and torsional structure},
  journal = {Molecular Physics},
  year = {1998},
  volume = {94},
  pages = {461-472},
  doi = {10.1080/002689798167971}
}
Abstract: The absorption spectrum of 1,-dichloroethane has been recorded under various experimental-conditions, between 50cm−1 and 10000cm−1 using Fourier transform spectroscopy, and-between 10800cm−1 and 17400cm−1 using optoacoustic laser spectroscopy. The assignment of the fundamental bands of the trans and gauche isomers was confirmed using in particular the results of recent ab initio calculations (El Youssoufi et al., 1998, Molec. Phys.,). The first overtone and combination bands were assigned for the first time using a variety of criteria including the band type and, in some cases, the spacing between clumps of rotational lines. Emphasis is placed on the CH progression of bands. Most of the results concern bands from the more abundant trans isomer, up to the near infrared range. Bands are tentatively assigned to the gauche species in the mid and near infrared regions and to the trans rotamer in the visible range. Vibrational frequencies and anharmonic parameters are obtained. © 1998 Taylor & Francis Group, LLC.
BibTeX:
@article{Youssoufi1998a,
  author = {Youssoufi, Y.E. and Lievin, J. and Vander Auwera, J. and Herman, M. and Fedorov, A. and Snavely, D.L.},
  title = {The ground electronic state of 1,-dichloroethane II. Experimental investigation of the fundamental and overtone vibrations},
  journal = {Molecular Physics},
  year = {1998},
  volume = {94},
  pages = {473-484},
  doi = {10.1080/002689798167980}
}
Abstract: Non-Hermitian complex effective Hamiltonians resulting from bound-continuous partitioning techniques are built from time dependent methods. We treat predissociation processes with a curve crossing. The energy dependent shift and half-width matrices are obtained simultaneously by a generalization of the wave packet Golden Rule treatment, as the real and imaginary parts of the Fourier transform of a memory kernel matrix. The latter contains auto- and cross-correlation functions. They are overlap integrals among the projections on the continuum of bound states multiplied by the interchannel coupling function responsible for the predissociation. These wave packets are propagated by the propagator of the sole continuous subspace. An approximate analytical expression of this correlation matrix is established for the harmonic/linear model. The numerical method is applied to the electronic predissociation of the MgCl A 2Π state, to a Morse/ exponential model and to a predissociation with two coupled repulsive decay channels. The comparison between the correlation time scales and the Golden Rule lifetimes is decisive so as to justify whether the memory kernel can be considered as an impulsive kernel. This Markovian approximation implies that the two time scales are well separated. In the energy domain, this corresponds to the introduction of a mean phenomenological effective Hamiltonian that neglects the energy variation of the discrete-continuous coupling elements. We observe that the separation of the time scales is effective for weakly open systems, but not for overlapping metastable states for which the perturbative-theory widths largely exceed the mean energy spacing. This confirms from a temporal viewpoint that a nonperturbative treatment should not neglect the energy dependence of the effective Hamiltonian, as currently assumed in the study of largely open systems. © 1997 American Institute of Physics.
BibTeX:
@article{Desouter-Lecomte1997,
  author = {Desouter-Lecomte, M. and Liévin, J.},
  title = {Memory kernels and effective Hamiltonians from time dependent methods. I. Predissociation with a curve crossing},
  journal = {Journal of Chemical Physics},
  year = {1997},
  volume = {107},
  pages = {1428-1440}
}
Abstract: We report on the first detailed rovibrational analysis in 1,2-dichloroethane. It concerns the a-type v16 absorption band of gaseous trans-1,2-dichloroethane at 1232 cm-1, which we have recorded using a Fourier transform interferometer, under room temperature and jet-cooled experimental conditions. The rotational analysis of the almost diatomic-like prominent R and P structures in v16 is performed for trans-1,2-12C2H4 35Cl2 and trans-1,2-12C2H4 35Cl37Cl. The nuclear spin statistics is discussed for various isotopomers and isomers of 1,2-dichloroethane. The complex absorption pattern observed at the band center is tentatively assigned in terms of overlapping Q branches, arising from fundamental bands involving different isotopomers in natural abundance (with 35Cl and 37Cl), and from related hot bands involving the three lowest vibrational modes in the molecule, v6, v10, and v18. © 1997 Academic Press.
BibTeX:
@article{ElYoussoufi1997,
  author = {El Youssoufi, Y. and Georges, R. and Liévin, J. and Herman, M.},
  title = {High-Resolution Spectroscopic Investigation of v16 in trans-1,2-Dichloroethane},
  journal = {Journal of Molecular Spectroscopy},
  year = {1997},
  volume = {186},
  pages = {239-245}
}
Abstract: Extensive ab initio calculations are performed concerning N2O4 in the ground electronic state, at the MP4 and CMRCI levels of theory, using the 6-31G* and cc-pVTZ basis sets. Special care is devoted to internal degrees of freedom characterizing the quasi van der Waals NN bond, namely the torsion and the NN stretch vibrational modes. The role of the methodology is investigated with the help of previous literature results. It is shown that most properties are significantly better described by MP4 than by MP2, but that a variational multireference method, like CMRCI, is however required for all properties linked to the NN bond. The ab initio vibrational analysis is merged with the one of absorption spectra recorded at medium resolution between 700 and 7000 cm-1, using a Fourier transform interferometer. The resulting set of effective vibrational frequencies and anharmonicities is provided. The height of the torsional potential energy barrier is calculated to be 2000 cm-1, at the best level of theory (CMRCI/cc-pVTZ), in agreement with the highest experimental value available. © 1997 Elsevier Science B.V.
BibTeX:
@article{Elyoussoufi1997,
  author = {Elyoussoufi, Y. and Herman, M. and Liévin, J. and Kleiner, I.},
  title = {Ab initio and experimental investigation of the vibrational energy pattern in N2O4: The mid and near infrared ranges},
  journal = {Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy},
  year = {1997},
  volume = {53},
  pages = {881-894}
}
Abstract: Results from systematic multiconfiguration Hartree-Fock studies of the 2s2 1S0-2s3p 3Po 1 transitions in the Be-like sequence in the range of Z = 4-10 are reported for valence and core-valence models of correlation. The inclusion of core-valence correlation was essential for obtaining good agreement for the fine-structure splitting. The most accurate transition rates are in good agreement with the rates predicted from a semi-empirical analysis of experimental data.
BibTeX:
@article{FroeseFischer1997,
  author = {Froese Fischer, C. and Gaigalas, G. and Godefroid, M.},
  title = {The 2s2 1S0-2s3p 3P0 1 intercombination line in the Be-like sequence},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1997},
  volume = {30},
  pages = {3333-3342},
  doi = {10.1088/0953-4075/30/15/006}
}
Abstract: Results from systematic multiconfiguration Hartree-Fock studies of the 2s2 1S-2s3p1Po transition in the Be-like sequence in the range of 7 = 4-10 are reported for several models. The inclusion of core-valence correlation is essential for obtaining good agreement in the length and velocity form of the oscillator strength, the agreement improving with Z and reaching one part in 4000 for neon. In the case of Be, extensive cancellation occurs in the calculation of the dipole matrix element and correlation in the 1s2 core already plays a role at the 1% level of accuracy. The orbitals obtained from the core correlation model were used in a Breit-Pauli calculation mixing 1,3 Po states. The effect on the allowed transition data is included. The present calculations are generally in better agreement with semi-empirical values predicted from experiment than from experiment itself.
BibTeX:
@article{FroeseFischer1997a,
  author = {Froese Fischer, C. and Godefroid, M. and Olsen, J.},
  title = {Systematic studies of the 2s2 1S0-2s3p1Po 1 transition in the Be-like sequence},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1997},
  volume = {30},
  pages = {1163-1172},
  doi = {10.1088/0953-4075/30/5/011}
}
Abstract: The hyperfine structure constants for the 1s 22s 22p 3 - 4S ground state in nitrogen and the 1s 22s 22p 33s 5S o excited state in oxygen are calculated using the MCHF Atomic Structure Package. The single excitation picture is explored through the use of compact wave functions allowing radial non-orthogonalities. Electron correlation is described through numerical multiconfiguration Hartree-Fock calculations for configuration expansions obtained by allowing all single and double excitations from the reference configuration to an active set of orbitals. The latter is increased in a systematic way allowing the convergence of the hyperfine parameters to be studied. Three- and four-particle effects are shown to be important and are taken into account in a sequence of large configuration interaction calculations. The final results are in good agreement with experiment. © Springer-Verlag 1997.
BibTeX:
@article{Godefroid1997,
  author = {Godefroid, M.R. and Van Meulebeke, G. and Jönsson, P. and Froese Fischer, C.},
  title = {Large-scale MCHF calculations of hyperfine structures in nitrogen and oxygen},
  journal = {Zeitschrift fur Physik D-Atoms Molecules and Clusters},
  year = {1997},
  volume = {42},
  pages = {193-201}
}
Abstract: The analysis of the Brillouin conditions in a chain of groups is used to explain why self-consistent field (SCF), multiconfigurationai SCF (MCSCFX or configuration interaction (CI) methods can lead to an unbalanced description of the potential energy hypersurfaces along symmetry-broken pathways. A Wigner-Racah formulation of the generalized Brillouin theorem is the appropriate theoretical tool for performing such an analysis. We apply this procedure to a Renner-Teller splitting in BH2 and to a pseudo-Jahn-Teller conical intersection in PO2. A systematic ab initio study of both systems leads to the definition of compact CASSCF wave functions which ensure a balanced description of the ground Born-Oppenheimer potential enerev surfaces. © 1997 John Wiley & Sons, Inc.
BibTeX:
@article{Lievin1997,
  author = {Liévin, J. and Vaeck, N.},
  title = {Use of symmetry-adapted Brillouin theorem to analyze the variational content of molecular wave functions along potential energy surfaces: Application to BH2 and PO2},
  journal = {International Journal of Quantum Chemistry},
  year = {1997},
  volume = {62},
  pages = {521-541}
}
BibTeX:
@article{Smith1997,
  author = {Smith, S.J. and Sutcliffe, B.T.},
  title = {The Development of Computational Chemistry in the United Kingdom},
  journal = {Reviews in Computational Chemistry},
  year = {1997},
  volume = {10},
  pages = {271-316}
}
Abstract: Modern highly accurate electronic structure calculations are undertaken with a view to elucidating molecular structure. For this to be possible the relationship of nuclear motion to electronic structure must be specified. An outline of how this specification might be made and some of the problems encountered in making it are discussed. © 1997 Academic Press Inc.
BibTeX:
@article{Sutcliffe1997,
  author = {Sutcliffe, B.T.},
  title = {The Nuclear Motion Problem in Molecular Physics},
  journal = {Advances in Quantum Chemistry},
  year = {1997},
  volume = {28},
  pages = {65-80},
  doi = {10.1016/S0065-3276(08)60207-5}
}
Abstract: A comparison between the recent measurements [Musielok et al., Phys. Rev. A53, 3122 (1996)] of the relative oscillator strengths for all lines in the three multiplets comprising the 2p3s-2p3p transition array in N II, and theoretical configuration interaction calculations performed with the CIV3 code [Bell et al., Physica Scripta 52, 240 (1995)] shows that, although the agreement between the experimental data and the theoretical results is good for allowed transitions, some unexpected deviations occur for the intersystem lines. In this work, we show that the previous theoretical work can be improved and some significant discrepancies with experiment eliminated by increasing the accuracy of the calculated energy difference between the 2p3s 3P1 o and 1P1 o states. This is achieved by the inclusion of additional orbitals and configurations together with adjustment of the diagonal matrix elements of the Hamiltonian. The new theoretical results for the transitions 2p3s 1,2PJ o→2p2 and 2p3p LSJ are compared with other theoretical work and with the experimental data.
BibTeX:
@article{Vaeck1997,
  author = {Vaeck, N. and Fleming, J. and Bell, K.L. and Hibbert, A. and Godefroid, M.R.},
  title = {The 2s22p3s 1,3PJ o→2s22p2 and 2s22p3p LSJ oscillator strengths in N II},
  journal = {Physica Scripta},
  year = {1997},
  volume = {56},
  pages = {603-608}
}
Abstract: The electronic redistribution of an ion or atom induced by a sudden recoil of the nucleus occurring during the emission or capture of a neutral particle is theoretically investigated. For one-electron systems, analytical expressions are derived for the electronic transition probabilities to bound and continuum states. The quality of a B-spline basis set approach is evaluated from a detailed comparison with the analytical results. This numerical approach is then used Io study the dynamics of two-electron systems (neutral He and Ne 8+) using correlated wavefunctions for both the target and daughter ions. The total transition probabilities to discrete states, autoionizing states and direct single- and double-ionization probabilities are calculated from the pseudospectra. Sum rules for transition probabilities involving an initial bound state and a complete final series are discussed.
BibTeX:
@article{Wauters1997,
  author = {Wauters, L. and Vaeck, N. and Godefroid, M. and Van Der Hart, H.W. and Demeur, M.},
  title = {Recoil-induced electronic excitation and ionization in one-and two-electron ions},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1997},
  volume = {30},
  pages = {4569-4589},
  doi = {10.1088/0953-4075/30/20/018}
}
Abstract: The spectrum of scandium was recorded in the infrared region using a high resolution Fourier transform spectrometer and a hollow-cathode discharge. Hyperfine structures of the lines connecting the 3d24s and 3d4s4p level systems of Sc45I were observed between 4000 and 5000cm-1. The structures were not completely resolved but the individual line contributions to the complex profiles were simulated using the 3d24s 4FJ hyperfine structure constants previously measured with a high precision by laser techniques. We investigate the possibility of extracting the hyperfine constants of the 3d4s4p levels from a least-squares fit of the line profiles, assuming a Doppler lineshape and theoretical relative intensities. New results are presented for 12 levels.
BibTeX:
@article{Aboussaid1996,
  author = {Aboussaïd, A. and Carleer, M. and Hurtmans, D. and Biémont, E. and Godefroid, M.R.},
  title = {Hyperfine structure of Sc I by infrared fourier transform spectroscopy},
  journal = {Physica Scripta},
  year = {1996},
  volume = {53},
  pages = {28-32}
}
Abstract: The body-fixed Hamiltonian developed here is expressed in terms of the atom's distance from and orientation with respect to the plane defined by the triatomic. © 1996 John Wiley & Sons, Inc.
BibTeX:
@article{Anderson1996,
  author = {Anderson, N. and Sutcliffe, B.T.},
  title = {The nuclear motion Hamiltonian for a tetratomic molecule considered as a combination of an atom and a triatom},
  journal = {International Journal of Quantum Chemistry},
  year = {1996},
  volume = {60},
  pages = {37-46}
}
Abstract: The transition between the diabatic and the adiabatic zero order representation when the electronic potential coupling increases, is studied in the partitioning method (PM) and in the complex coordinate method (CCM) implemented in a discrete variable representation (DVR). The model is a C+ type predissociation in a diatomic system with a crossing between a Morse potential energy curve and an exponentially repulsive curve. In the weak coupling regime (isolated diabatic metastable states), both methods confirm the linear variation of the resonance widths with the strength of the electronic interaction, as expected in a perturbative treatment. When the coupling is large in the diabatic representation (strong overlap regime), the formation of narrow resonances supported by the upper adiabatic potential can be related, in PM, to the process of avoided resonance overlapping among interfering states. The complete change of representation can be described in the initial diabatic basis set in PM. However, the full energy dependence of the discrete-continuous matrix elements must then be taken into account. The deformation and the final splitting of a diffuse spectral line .with increasing coupling is re-examined in terms of these energy dependent eigenvalues of the effective Hamiltonian. The use of the appropriate representation, either diabatic or adiabatic, according to the strength of the electronic coupling, has been found decisive in CCM so as to observe the correct migration of the resonance positions towards the zero order adiabatic states, and the decrease of their widths. No relevant results have been obtained for the intermediate strength of the coupling in CCM. Analytical expressions for the derivative coupling matrix elements (∂/∂R) in the fixed node DVR (corresponding to the particle-in-a-box wave functions) have been established. © 1996 American Institute of Physics.
BibTeX:
@article{Brems1996,
  author = {Brems, V. and Desouter-Lecomte, M. and Liévin, J.},
  title = {Avoided resonance overlapping beyond the energy independent formalism. II. Electronic predissociation},
  journal = {Journal of Chemical Physics},
  year = {1996},
  volume = {104},
  pages = {2222-2236}
}
Abstract: The series solution method used by H. Cox, S. J. Smith and B. T. Sutcliffe (1994, Phys. Rev. A, 49, 4520, 4533) to obtain extremely accurate eigenvalues and eigenvectors for the lowest singlet and triplet states of low Z helium-like systems has been applied to the ground 1S state of the positronium negative ion. Secular determinatnts of up to size 2847 × 2847 have been solved to give a ground state energy of 0·262 005 070 231 742 au. This agrees to 12 decimal places with the most accurate literature value reported by Y. K. Ho (1993, Phys. Rev. A, 48, 4780). Various expectation values involving the interparticle distances have also been evaluated. We estimate the positron-electron annihilation rate Г as 2·086 1223 ns-1. This is in agreement with the most accurate literature value of 2·086 1222 ± 5 × 10-7 (Ho, 1993, Phys. Rev. A, 48, 4780) and the experimental value of 2·09 ± 9 × 10-2 (Mills, 1983, Phys. Rev. Lett., 50, 671). © 1996 Taylor & Francis Group, LLC.
BibTeX:
@article{Cox1996,
  author = {Cox, H. and Sinclair, P.E. and Smith, S.J. and Sutcliffe, B.T.},
  title = {Some calculations on the ground 1S state of the positronium negative ion},
  journal = {Molecular Physics},
  year = {1996},
  volume = {87},
  pages = {399-406},
  doi = {10.1080/00268979600100261}
}
Abstract: Intercombination line transition rates between n = 2 levels of B II, O V, Ne VII and Mg IX have been calculated using the configuration interaction code CIV3. The recommended A-values for the 2s2p 3P1 o-2s2 1S0 intercombination lines are 9.73 s-1 for B II, 2280 s-1 for O V, 19 204 s-1 for Ne VII and 97 242 s-1 for Mg IX. We estimate that the accuracy of these values is better than 2 per cent. Calculations of the M2, E2 and M1 transitions have also been carried out for these ions and for C III.
BibTeX:
@article{Fleming1996a,
  author = {Fleming, J. and Bell, K.L. and Hibbert, A. and Vaeck, N. and Godefroid, M.R.},
  title = {Forbidden transitions in B II, C III, O V, Ne VII and Mg IX},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {1996},
  volume = {279},
  pages = {1289-1293}
}
Abstract: The oscillator strength of the resonance transition 2s2 1S0-2s2p 1Po1 in neutral beryllium is evaluated using two independent codes: CIV3 and MCHF. Two separate approaches are executed using the code CIV3, which uses a common set of orbitals, the inclusion of valence, core-valence and core-core correlation being approached in different ways. In the MCHF scheme the wavefunctions of the two states are optimized independently. The convergence of the MCHF results with respect to the addition of orbital functions is considered in some detail. This convergence, together with the results of the CIV3 calculates, lead us to recommend a value of 1.375 for the oscillator strength, with an estimated uncertainty of less than 0.5%. This agrees closely with other recent extensive calculations but is 2.5% higher than the value derived from beam-foil experiments.
BibTeX:
@article{Fleming1996b,
  author = {Fleming, J. and Godefroid, M.R. and Bell, K.L. and Hibbert, A. and Vaeck, N. and Olsen, J. and Jönsson, P. and Froese Fischer, C.},
  title = {The 2s2 1S-2s2p 1Po resonance line in neutral beryllium},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1996},
  volume = {29},
  pages = {4347-4363},
  doi = {10.1088/0953-4075/29/19/009}
}
Abstract: Extensive configuration-interaction calculations have been performed to obtain oscillator strengths for the resonance line of the ions of the beryllium isoelectronic sequence up to nuclear charge Z = 12. Valence, corevalence and core-core correlation effects are taken into account and relativistic effects are incorporated using the Breit-Pauli scheme. The present results are believed to be accurate to better than 1%.
BibTeX:
@article{Fleming1996,
  author = {Fleming, J. and Vaeck, N. and Hibbert, A. and Bell, K.L. and Godefroid, M.R.},
  title = {Oscillator strengths for the resonance line of ions in the beryllium isoelectronic sequence},
  journal = {Physica Scripta},
  year = {1996},
  volume = {53},
  pages = {446-453}
}
Abstract: The v1 fundamental band in N2O3 was recorded in absorption at high spectral resolution with a Fourier Transform interferometer, under jet cooled experimental conditions. The rotational structure, corresponding to 44 K rotational temperature, could be analysed, leading to a set of precise upper state parameters. The absence of b-type lines in the spectrum, expected to occur from the direction of the Q1 normal coordinate with respect to the principal axes of inertia, is fully justified by ab initio calculations performed at the MP2/6-31G * level, confirming the decisive role of the polarizing NO2 chromophore in tilting the corresponding induced dipole moment towards the direction of the a axis. The calculations also provide equilibrium geometry parameters.
BibTeX:
@article{Georges1996,
  author = {Georges, R. and Liévin, J. and Herman, M. and Perrin, A.},
  title = {The v1 band in N2O3},
  journal = {Chemical Physics Letters},
  year = {1996},
  volume = {256},
  pages = {675-678},
  doi = {10.1016/0009-2614(96)00510-6}
}
Abstract: The progress achieved over the last few years in variational Multiconfiguration Hartree-Fock and Configuration Interaction calculations is reviewed. The high level of accuracy which can be reached in the ab initio calculation of atomic properties of light systems is illustrated through the results of calculations of isotope shifts, hyperfine structures and transition probabilities. The active space method and associated restricted active space methods allowing systematic calculations from which the accuracy of the studied property can be estimated will be discussed. We exemplify quality checks through results in small systems for which spectroscopic accuracy is often required. For transition probabilities, recent progress derived from new algorithm developments allowing independent optimization of the states is emphasized.
BibTeX:
@conference{Godefroid1996,
  author = {Godefroid, M.R. and Fischer, C.F. and Jönsson, P.},
  title = {Multiconfiguration Hartree-Fock calculations of atomic properties in light atoms},
  journal = {Physica Scripta T},
  year = {1996},
  volume = {65},
  pages = {70-83}
}
Abstract: Results from systematic multiconfiguration Hartree-Fock calculations of transition probabilities, isotope shifts and hyperfine structures of the 1s22s22p 2Po-1s22s23s 2S and 1s22s22p 2Po-1s22s2p2 2D transitions in B I, the 1s22s22p 2Po-1s22s2p2 2(S, P, D) transitions in C II and the 1s22s22p2 3P-1s22s2p3 3Do transition in C I are reported. Higher-order correlation effects beyond the pair-correlation approximation are shown to be important for the transition probabilities, and are included in large configuration interaction calculations. For all the transitions except one, the agreement between the length and velocity forms of the weighted oscillator strength is better than 0.4%. The present results are believed to be substantially more accurate than those of other theories.
BibTeX:
@article{Joensson1996,
  author = {Jönsson, P. and Froese Fischer, C. and Godefroid, M.R.},
  title = {Accurate calculations of transition probabilities, isotope shifts and hyperfine structures for some allowed 2s22pn-2s2pn+1 transitions in B I, C II and C I},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1996},
  volume = {29},
  pages = {2393-2412},
  doi = {10.1088/0953-4075/29/12/007}
}
Abstract: Results from large-scale multiconfiguration Hartree-Fock (MCHF) and configuration-interaction (CI) calculations of the transition probability and hyperfine structures in the sodium 3s 2S - 3p 2P resonance transition are presented. In the calculations the orbital sets of the initial and final state wave functions were not restricted to be the same, but were optimized independently. The evaluation of the transition matrix elements was done using a technique where the two orbital sets are transformed so as to become biorthonormal, in which case standard Racah algebra can be used. Three-particle effects were taken into account in the CI calculations and were found to be important for the hyperfine structures, but less important for the transition probability. The calculated transition probability is in perfect agreement with the most recent experimental values, thus resolving the long-standing disagreement between theory and experiment. Also the 3s 2S1/2 and 3p 2P1/2,3/2 hyperfine interaction constants are in very good agreement with available experimental values.
BibTeX:
@article{Joensson1996a,
  author = {Jönsson, P. and Ynnerman, A. and Fischer, C.F. and Godefroid, M.R. and Olsen, J.},
  title = {Large-scale multiconfiguration Hartree-Fock and configuration-interaction calculations of the transition probability and hyperfine structures in the sodium resonance transition},
  journal = {Physical Review A - Atomic, Molecular, and Optical Physics},
  year = {1996},
  volume = {53},
  pages = {4021-4030}
}
Abstract: The microwave spectrum of acetaldehyde is critically reviewed and supplemented with spectral frequency calculations derived from the rotation-internal rotation analysis. A simultaneous analysis of the torsional ground state, vt = 0, and first and second torsionally excited states, vt = 1 and 2, was carried out. The primary objective of this review is to provide radio astronomers with complete spectral coverage over the range of 900 MHz to 500 GHz for the ground state and covering rotational quantum number, J, from 0 to 26. © 1996 American Institute of Physics and American Chemical Society.
BibTeX:
@article{Kleiner1996,
  author = {Kleiner, I. and Lovas, F.J. and Godefroid, M.},
  title = {Microwave spectra of molecules of astrophysical interest. XXIII. Acetaldehyde},
  journal = {Journal of Physical and Chemical Reference Data},
  year = {1996},
  volume = {25},
  pages = {1113-1116}
}
Abstract: The development of the idea of a chemical bond is traced from Frankland to Heitler and London and beyond with emphasis on how electrons came to be considered essential to explaining the bond. © 1996 John Wiley & Sons, Inc.
BibTeX:
@article{Sutcliffe1996,
  author = {Sutcliffe, B.T.},
  title = {The development of the idea of a chemical bond},
  journal = {International Journal of Quantum Chemistry},
  year = {1996},
  volume = {58},
  pages = {645-655}
}
Abstract: The electronic rearrangement resulting from the β decay of 6He has been calculated in the framework of the sudden approximation using a numerical B-spline basis set approach. We have calculated the excitation probabilities to the final discrete states of 6Li+ (including to the doubly excited autoionizing states) as well as the total probabilities for single and double ionization. The correct treatment of electronic correlation in the framework of the sudden approximation is shown to modify the PK value (the probability that an atomic K vacancy is created) by more than 2%.
BibTeX:
@article{Wauters1996,
  author = {Wauters, L. and Vaeck, N.},
  title = {Study of the electronic rearrangement induced by nuclear transmutations: A B-spline approach applied to the β decay of 6He},
  journal = {Physical Review C - Nuclear Physics},
  year = {1996},
  volume = {53},
  pages = {497-500},
  doi = {10.1103/PhysRevC.53.497}
}
Abstract: We are investigating the hyperfine quenching of 1s2p 3P0o for the three heliumlike ions F7+19, Na9+23, and Al11+27 in the multiconfigurational Hartree-Fock-Breit-Pauli scheme. The configuration expansions are generated with the active-space method and are increased in a systematic way, allowing the convergence of the calculated parameters to be studied. A careful comparison is done with the pioneering work of Mohr using a perturbation approach [Beam-Foil Spectroscopy, Atomic Structure and Lifetimes, edited by I. Sellin and D. Pegg (Plenum, New York, 1976), Vol. 1, pp. 97-103]. In the present calculations the orbital and spin-dipole magnetic contributions, which were previously neglected, are added to the dominant Fermi contact interaction term and a detailed analysis of the hyperfine induced transition rate is done in order to learn how to get an accurate description of the property in the multiconfiguration Hartree-Fock-Breit-Pauli approximation. © 1995 The American Physical Society.
BibTeX:
@article{Aboussaid1995,
  author = {Aboussaïd, A. and Godefroid, M.R. and Jönsson, P. and Froese Fischer, C.},
  title = {Multiconfigurational Hartree-Fock calculations of hyperfine-induced transitions in heliumlike ions},
  journal = {Physical Review A},
  year = {1995},
  volume = {51},
  pages = {2031-2039},
  doi = {10.1103/PhysRevA.51.2031}
}
Abstract: A flew isotope shift program, part of the mchf atomic structure package, has recently been written. The program calculates the isotope shift of an atomic level from multiconfiguration Hartree-Fock (mchf) or configuration interaction (Ci) wavefunctions and is specially designed to be used with very large ci expansions, for which angular data cannot be stored on disk. To explore the capacity of the program, large-scale isotope shift calculations have been performed for the 1s22s2S and Is22p2P levels in C tv and for the ls22s22p2 S, ls22s22p3s ‘P, ls22s22p2 3P and ls22s2p3 5S levels in C t. From the isotope shifts of these levels theMC-i2C isotope shifts were calculated for the Is22s2S-ls22p2P transition in C iv and for the Is22s22p2 1 S-ls22s22p3sJP and ls22s22p2 3P-!s22s2p3 5S transitions in C i. The calculated transition isotope shifts are in very good agreement with experimental values, available for the C i transitions. As a check on the overall quality of the wavefunctions, the hyperfine structure interaction constants were calculated for the levels in C tv. © 1995 IOP Publishing Ltd.
BibTeX:
@article{Carlsson1995,
  author = {Carlsson, J. and Jonsson, P. and Godefroid, M.R. and Fischer, C.F.},
  title = {Accurate multiconfiguration hartree-fock calculations of isotope shifts in c i and c iv},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1995},
  volume = {28},
  pages = {3729-3740},
  doi = {10.1088/0953-4075/28/17/012}
}
Abstract: An extension of the multiconfigurational SCF approach for the resolution of the vibrational problem is presented; it follows the philosophy of the CASSCF method developed in Quantum Chemistry. The new method allows a more complete treatment of anharmonic mode couplings, converges much faster and gives a clearer physical insight of vibrational interactions. This is exemplified by the calculation of infrared transition moments in the H2O and D2O isotopomers of the water molecule. It is shown how this property varies with the quality of the wave function when vibrational resonances occur. A detailed analysis by means of this new VCASSCF method demonstrates the crucial importance of excited bending oscillators in the intensity of some pure stretching transitions. © 1995 Springer-Verlag.
BibTeX:
@article{Culot1995,
  author = {Culot, F. and Laruelle, F. and Liévin, J.},
  title = {A vibrational CASSCF study of stretch-bend interactions and their influence on infrared intensities in the water molecule},
  journal = {Theoretica Chimica Acta},
  year = {1995},
  volume = {92},
  pages = {211-226},
  doi = {10.1007/BF01125947}
}
Abstract: The interaction of overlapping resonances is studied in the case of a vibrational predissociation in a linear molecule. The energy independent approach rests on the neglect of the variation of the coupling elements with the energy in the continuum. It predicts the formation of trapped and short-lived decay modes when resonances overlap. The relevance of this prediction is discussed on the basis of results obtained from two different methods going beyond this energy independent formalism. The first one consists in searching the solutions of the implicit equation derived from the Feshbach partitioning method, taking into account the full energy dependence of the local effective Hamiltonian Heff(E). The second one is the variational complex coordinate method (CCM), implemented in a discrete variable representation (DVR). The results demonstrate that the energy dependency enhances the trapping effect. The distribution of the resonance energies in the complex plane is different from the prediction of the energy independent formalism. The fast modes are found to be slower than expected. Their position is also completely shifted. The mean width is not constrained by a sum rule which is characteristic of the energy independent approximation. © 1995 American Institute of Physics.
BibTeX:
@article{Desouter-Lecomte1995,
  author = {Desouter-Lecomte, M. and Liévin, J. and Brems, V.},
  title = {Avoided resonance overlapping beyond the energy independent formalism. I. Vibrational predissociation},
  journal = {The Journal of Chemical Physics},
  year = {1995},
  volume = {103},
  pages = {4524-4537}
}
Abstract: E1, M2, M1 and E2 rates of transitions between n = 2 levels of N IV have been calculated using the two independent codes CIV3 and MCHF. Convergence of each of the approaches has been studied and comparisons made as the complexity of the calculations increases to include valence, core-valence and core-core correlation. The agreement between the two methods is sufficiently good to allow us to set quite narrow uncertainty bars. For the 1S-1P0 resonance line, our recommended f-value is 0.609 with an estimated uncertainty of 0.002, while our recommended A-value for the 1S0 -3P0 1 intercombination line is 580 s-1 with an estimated uncertainty of 10 s-1.
BibTeX:
@article{Fleming1995,
  author = {Fleming, J. and Brage, T. and Bell, K.L. and Vaeck, N. and Hibbert, A. and Godefroid, M.R. and Froese Fischer, C.},
  title = {Systematic studies of N IV transitions of astrophysical importance},
  journal = {Astrophysical Journal},
  year = {1995},
  volume = {455},
  pages = {758-768}
}
Abstract: A new method to deal with nonorthogonalities in transition calculations has been implemented and tested. Large-scale transition calculations using the multiconfiguration Hartree-Fock (MCHF) method have been performed for the resonance line of B II at 1362 Å. In these calculations the orbital sets of the initial and final-state wavefunctions have not been assumed to be equal but have been optimized independently. The calculated weighted multiplet oscillator strength gf = 0.999 has an estimated uncertainty of less than 0.5%. Together with the previously calculated isotope shift and hyperfine structure (Jönsson, Johansson, & Froese Fischer 1994), all the important atomic parameters needed for a detailed modeling of the B II resonance line in high-resolution astrophysical spectra are now available with high accuracy.
BibTeX:
@article{Godefroid1995,
  author = {Godefroid, M. and Olsen, J. and Jönsson, P. and Fischer, C.F.},
  title = {Accurate multiconfiguration Hartree-Fock calculations of oscillator strengths in light atoms: The boron (B II) line at 1362 Å},
  journal = {Astrophysical Journal},
  year = {1995},
  volume = {450},
  pages = {473-476}
}
Abstract: Complementary experimental, ab initio and dynamical investigations are reported on monodeuteroacetylene, C2HD (X̃1Σ+). All experimental spectroscopic results previously reported in the literature on C2HD, i.e. from 500 to 16000 cm-1 are gathered. New results are included, which are obtained from the analysis of absorption data recorded with a Fourier transform interferometer at high resolution between 4600 and 9000 cm-1. The presence of numerous weak bands along the whole spectral range is analysed in terms of systematic anharmonic couplings. The entire set of energy data is then used to produce thirty-five vibrational frequencies and anharmonicities from a fit of the vibrational energies to a Dunham-type expansion, and the vibrational level density is extrapolated, up to higher energy. One- and two-dimensional potential energy and dipole moment surfaces refined from new ab initio results are fitted to a selected set among those experimental data, associated to the stretch overtones. The iterative procedure involving an original package of computer programs is described. The evolution of the overtone intensities of the CH and CD stretches, up to η = 4, is interpreted on that basis in terms of electric and mechanical anharmonicity contributions. Eventually, dynamical aspects are studied thanks to the newly introduced vibrograms, which allow to obtain the time recurrences of the vibrational dynamics. Using the Gutzwiller and Berry-Tabor trace formulas, these vibrational recurrences are semiclassically assigned to periodic orbits of the classical Hamiltonian given by the Dunham expansion. © 1995.
BibTeX:
@article{Lievin1995,
  author = {Liévin, J. and Abbouti Temsamani, M. and Gaspard, P. and Herman, M.},
  title = {Overtone spectroscopy and dynamics in monodeuteroacetylene (C2HD)},
  journal = {Chemical Physics},
  year = {1995},
  volume = {190},
  pages = {419-445},
  doi = {10.1016/0301-0104(94)00378-N}
}
Abstract: Individual orbital optimization of wave functions for the initial and final states produces the most accurate wave functions for given expansions, but complicates the calculation of transition-matrix elements since the two sets of orbitals will be nonorthogonal. The orbital sets can be transformed to become biorthonormal, in which case the evaluation of any matrix element can proceed as in the orthonormal case. The transformation of the wave-function expansion to the new basis imposes certain requirements on the wave function, depending on the type of transformation. An efficient and general method was found a few years ago for expansions in determinants, spin-coupled configurations, or configuration state functions for molecules belonging to the D2h point group or its subgroups. The method requires only that the expansions are closed under deexcitation and thus applies to restricted active space wave functions. This type of expansion is efficient for correlation studies and includes many types of expansions as special cases. The above technique has been generalized to the atomic, symmetry adapted case requiring the treatment of degenerate shells nlN, with arbitrary occupation numbers 0≤N≤4l+2. A computer implementation of the algorithm in the multiconfiguration Hartree-Fock atomic-structure package for atoms allows the calculation of transition moments for individually optimized states. An application is presented for the B i 1s22s22p 2Po→1s22s2p2 2D electric dipole transition probability, which is highly sensitive to core-polarization effects. © 1995 The American Physical Society.
BibTeX:
@article{Olsen1995,
  author = {Olsen, J. and Godefroid, M.R. and Jönsson, P. and Malmqvist, P.A. and Fischer, C.F.},
  title = {Transition probability calculations for atoms using nonorthogonal orbitals},
  journal = {Physical Review E},
  year = {1995},
  volume = {52},
  pages = {4499-4508},
  doi = {10.1103/PhysRevE.52.4499}
}
Abstract: High resolution profiles of neutral vanadium lines have been recorded in the infrared region (1800-9000 cm-1) by Fourier transform spectroscopy. 106 transitions showing resolvedor partially resolved hyperfine profiles have been analysed. An investigation of these structureshas allowed the deduction of magnetic dipole constants for 101 levels. For 69 levels the resultsobtained are new. The results of the present work have been compared with the few datapreviously published in the literature and they are generally in good agreement. © 1995 IOP Publishing Ltd.
BibTeX:
@article{Palmeri1995,
  author = {Palmeri, P. and Biémont, E. and Aboussaid, A. and Godefroid, M.},
  title = {Hyperfine structure of infrared vanadium lines},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1995},
  volume = {28},
  pages = {3741-3752},
  doi = {10.1088/0953-4075/28/17/013}
}
Abstract: The development of the idea of a potential energy surface is examined in the context of solutions to the full quantum mechanical problem specified by the Schrödinger Hamiltonian expressed in laboratory-fixed coordinates. © 1995 Elsevier Science B.V. All rights reserved.
BibTeX:
@article{Sutcliffe1995,
  author = {Sutcliffe, B.T.},
  title = {The idea of a potential energy surface},
  journal = {Journal of Molecular Structure: THEOCHEM},
  year = {1995},
  volume = {341},
  pages = {217-235},
  doi = {10.1016/0166-1280(95)04125-P}
}
Abstract: We present calculations of autoionization lifetimes for ‘hollow’ nitrogen atoms with and without a core of one or two Is electrons. We have observed a very similar patternin theNdependence of the lifetimes for all lsnp configurations withM= 0, 1 and 2, n   2, 3, 4.5, 6, 7 and 10 andN =2, 3, 4, 5 and 6. Also some IsntNconfigurations witht 1have been considered as well as configurations with mixed values ofn.For configurations withall the electrons in the samenshell we have found that the average lifetime inneutralsystemsis very short, typically of the order of 3-5 x 10-16 for n = 3 to 7. The same applies toconfigurations with mixed values ofn(of the order of 1-6 x 10-16s for n = 3 to 7). Wefind that the importance of electron correlation increases dramatically withnandNbut that theaverage autoionization decay rates do not change. The configurations studied are of interest, forexample, in the study of processes that occur during neutralization of highly charged nitrogenions at surfaces. © 1995 IOP Publishing Ltd.
BibTeX:
@article{Vaeck1995,
  author = {Vaeck, N. and Hansen, J.E.},
  title = {Auger decay of hollow nitrogen atoms},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1995},
  volume = {28},
  pages = {3523-3543},
  doi = {10.1088/0953-4075/28/16/008}
}
Abstract: Calculations concerning the competition between radiative and non-radiative decay for doubly-excited 4lnl' (n = 4.5) singlet states in Ne8+ are reported. Recent coincidence experiments have been interpreted as showing that for the 414/' states in Ne8+, as well as in the isoelectronic N5+ and O6+ systems, radiation contributes more than 50% to the total decay. The 4l4l' states in Ne8+ are, as in N5+ and O6+, degenerate with the 3ln!' Rydberg states and a considerable mixing exists between the two, which leads to an increase in the radiative decay probability. In the free Ne8+ ion we find that radiative decay accounts for 29% of the total decay for the singlet terms assuming a statistical population distribution. The results vary considerably between terms and the total radiative yield is strongly dependent on the initial population distribution. The branching ratio is similar to the ratio obtained under similar conditions for O6+. The similarity is ascribed to two competing effects: the lowering of the 4/41' states relative to the 3Ini' series with increasing Z, which favours decay through autoionization, and the Z4 behaviour of the radiative decay rates, which has the opposite effect. The free ion results are compared to results including the auto-transfer to Rydberg states (atr) mechanism. In N5+ we have shown that this effect leads to an appreciable reduction in the radiative yield. For Ne8+, the ATR mechanism is less important but we conclude that also here the effect on average is a (small) reduction in radiative yield. This is because the atr mechanism is usually so effective that the 4l4l' population is transferred to low Rydberg states. These autoionize in light ions while they have a larger probability for radiative decay with increasing Z. This seems to account for a large part of the difference between the atr results in N5+ and Ne8+. We report the results of an alternative approach in which part of the collision dynamics is included and we find that the atr model is rather sensitive to a number of parameters, which at the moment are not known very well. For the 4l5l' states, which are located above the N = 3 threshold, radiative decay accounts for 6% of the total decay, much less than for the 4l4l' states, due to the opening of autoionization channels to the N = 3 thresholds for the 4l5l' states. Assuming a statistical population distribution, the theoretical results are in clear disagreement with recent observations for both 4l4l' and 4l5l' manifolds. However, we conclude that it is necessary to obtain a more definite idea about the real population distribution before it is possible to make meaningful comparisons with the observed radiative yields. © 1995 IOP Publishing Ltd.
BibTeX:
@article{VanDerHart1995,
  author = {Van Der Hart, H.W. and Vaeck, N. and Hansen, J.E.},
  title = {Radiative stabilization of the doubly-excited 4l4l' and 4l5l' singlet terms in ne8+},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1995},
  volume = {28},
  pages = {5207-5228},
  doi = {10.1088/0953-4075/28/24/007}
}
Abstract: The body-fixed Hamiltonian for a trimer of polyatomic monomers is expressed in terms of the distances between the monomer centers of mass and of the orientation angles of the monomers relative to the body-fixed frame. The particular case where the monomers are water molecules is considered in some detail. In this work we attempt to assess the possibility of using a computer algebra system to aid in the evaluation of the angular matrix elements. © 1995 American Institute of Physics.
BibTeX:
@article{Xantheas1995,
  author = {Xantheas, S.S. and Sutcliffe, B.T.},
  title = {The Hamiltonian for a weakly interacting trimer of polyatomic monomers},
  journal = {The Journal of Chemical Physics},
  year = {1995},
  volume = {103},
  pages = {8022-8030}
}
Abstract: This paper presents a discussion of some programs written in the computer algebra language Maple and in the C language for solving the body-fixed Schrödinger equation for three particles with Coulomb interaction in perimetric coordinates by means of a series solution. © 1994.
BibTeX:
@article{Cox1994,
  author = {Cox, H. and Smith, S.J. and Sutcliffe, B.T.},
  title = {An application of the computer algebra system Maple for calculations on atomic and molecular systems},
  journal = {Computer Physics Communications},
  year = {1994},
  volume = {84},
  pages = {186-200},
  doi = {10.1016/0010-4655(94)90211-9}
}
Abstract: The series solution method developed by Pekeris [Phys. Rev. 112, 1649 (1958); 115, 1216 (1959)] for the Schrödinger equation for two-electron atoms, as generalized by Frost et al. [J. Chem. Phys. 41, 482 (1964)] to handle any three particles with a Coulomb interaction, has been used. The wave function is expanded in triple orthogonal set in three perimetric coordinates. From the Schrödinger equation an explicit recursion relation for the coefficients in the expansion is obtained, and the vanishing of the determinant of these coefficients provides the condition for the energy eigenvalues and for the eigenvectors. The Schrödinger equation is solved and the matrix elements are produced algebraically by using the computer algebra system maple. The substitutions for a particular atom and diagonalization were performed by a program written in the c language. Since the determinant is sparse, it is possible to go to the order of 1078 as Pekeris did without using excessive memory or computer CPU time. By using a nonlinear variational parameter in the expression used to remove the energy, nonrelativistic energies, within the fixed-nucleus approximation, have been obtained. For the ground-state singlet 1 1S state, this is of the accuracy claimed by Frankowski and Pekeris [Phys. Rev. 146, 46 (1966); 150, 366(E) (1966)] using logarithmic terms for Z from 1 to 10, and for the triplet 2 3S state, energies have been obtained to 12 decimal places of accuracy, which, with the exception of Z=2, are lower than any previously published, for all Z from 3 to 10. © 1994 The American Physical Society.
BibTeX:
@article{Cox1994a,
  author = {Cox, H. and Smith, S.J. and Sutcliffe, B.T.},
  title = {Some calculations on the ground and lowest-triplet state of helium in the fixed-nucleus approximation},
  journal = {Physical Review A},
  year = {1994},
  volume = {49},
  pages = {4520-4532},
  doi = {10.1103/PhysRevA.49.4520}
}
Abstract: The method described in the preceding paper for the solution of two-electron atoms, which was used to calculate the 1 1S and 2 3S states of helium and heliumlike atoms within the fixed-nucleus approximation, has been applied to the case where all three particles are in relative motion. The solutions in the present case automatically include the effects of the mass polarization term and are compared with the results obtained for the term by using first-order perturbation theory with the fixed-nucleus wave functions. The input data for a particular atom consist of the atomic number, as before, but now the corresponding mass of the nucleus must be given also. Nonrelativistic energies with the nuclear mass included in the calculation have been obtained for the 1 1S and 2 3S states for Z ranging from 1 to 10. The energy with the nucleus in motion can be expressed only to eight significant figures (SF's) given the accuracy with which the relevant physical constants are known at present. All the results given here are computed as if these constants were known to ten SF's so that errors not incurred due to rounding. Convergence of the energies to ten SF's for both the singlet and triplet state was reached with a matrix of size 444 for Z values from 2 to 10. Convergence for the H- ion was a little slower. © 1994 The American Physical Society.
BibTeX:
@article{Cox1994b,
  author = {Cox, H. and Smith, S.J. and Sutcliffe, B.T.},
  title = {Some calculations on the ground and lowest-triplet state of the helium isoelectronic sequence with the nucleus in motion},
  journal = {Physical Review A},
  year = {1994},
  volume = {49},
  pages = {4533-4539},
  doi = {10.1103/PhysRevA.49.4533}
}
Abstract: A new variational method for solving the molecular vibration problem is proposed. The so-called VMCSCF method (vibrational multiconfigurational self-consistent field) is based on the super-CI algorithm, previously developed in the framework of electronic ab initio calculations. This approach makes direct use of the generalised Brillouin theorem to ensure self-consistency. The method is dedicated to the study of strongly interacting states (vibrational resonances), which are one of the main sources of perturbation in vibrational spectra. The interest of the method to tackle resonance interactions is illustrated by means of test calculations performed on the water and formaldehyde molecules. © 1994 Springer-Verlag.
BibTeX:
@article{Culot1994,
  author = {Culot, F. and Liévin, J.},
  title = {A multiconfigurational SCF computational method for the resolution of the vibrational Schrödinger equation in polyatomic molecules},
  journal = {Theoretica Chimica Acta},
  year = {1994},
  volume = {89},
  pages = {227-250},
  doi = {10.1007/BF01225116}
}
Abstract: We investigate the stability of homonuclear diatomic molecules from H2 up to C2 and of the finite chains Hn (n≤5) and Hen (n≤4) immersed in very intense magnetic fields (B108 T). The atomic and molecular total energies are calculated within the one-dimensional Hartree-Fock approximation, using a Lagrange basis set associated with a Cartesian mesh. The stability of the molecules decreases beyond Li2 although all the studied molecules are found stable. The energy per atom of H and He finite chains stabilizes already for the small chain sizes that we have investigated. © 1994 The American Physical Society.
BibTeX:
@article{Demeur1994,
  author = {Demeur, M. and Heenen, P.-H. and Godefroid, M.},
  title = {Hartree-Fock study of molecules in very intense magnetic fields},
  journal = {Physical Review A},
  year = {1994},
  volume = {49},
  pages = {176-183},
  doi = {10.1103/PhysRevA.49.176}
}
Abstract: The atomic d shell is explored from the perspective of the quark model of the atom. In this scheme, all the states are generated by four statistically independent fictitious particles (the quarks), each with angular momentum 3/2, augmented by two parity labels. The detailed quark expansions are given for the two 2D terms of d3, and the results are compared to the classic analysis of Condon and Shortley (1935). Matrix elements of single-electron tensor operators and of the Coulomb interaction are calculated in the quark scheme, and the connection to the conventional approach is made. The diagonal sum method of Slater is applied to the quark states and extensions to many-electron operators are discussed. The correspondence between the quark model and the traditional method implies relations between various n-j symbols, and this is illustrated by two special cases. © 1994 IOP Publishing Ltd.
BibTeX:
@article{Godefroid1994,
  author = {Godefroid, M.R. and Judd, B.R. and Vaeck, N.},
  title = {Applying the quark model to the atomic d shell},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1994},
  volume = {27},
  pages = {3635-3652},
  doi = {10.1088/0953-4075/27/16/011}
}
Abstract: The body-fixed Hamiltonian for a triatomic molecule as given by Sutcliffe and Tennyson in 1991 had the molecule define the x-z plane. Here the relationship between this Hamiltonian and those in which the molecule defines other planes is exhibited. It is shown that in the Sutcliffe-Tennyson approach the original embedding is preferred. In this embedding the relative effectiveness of the finite- basis representation and the discrete-variable representation as a means of approximate solution are considered for rotationally excited states of water. © 1994 Taylor & Francis Ltd.
BibTeX:
@article{Henderson1994,
  author = {Henderson, J.R. and Tennyson, J. and Sutcliffe, B.T.},
  title = {The calculation of molecular spectra using finite-element methods},
  journal = {Philosophical Magazine B: Physics of Condensed Matter; Statistical Mechanics, Electronic, Optical and Magnetic Properties},
  year = {1994},
  volume = {69},
  pages = {1027-1036},
  doi = {10.1080/01418639408240171}
}
Abstract: A detailed discussion is presented of the relationships between four different molecular symmetry groups. i.e. D2, Cs, C3v, and C(m) 3v commonly used to discuss energy level symmetry species and electric-dipole selection rules for internal rotor problems in molecules with a symmetric rotor top and a frame with a plane of symmetry. paying particular attention to confusion arising from the fact that the smaller groups are not always subgroups of the larger, and the groups are applied to different parts of the internal rotation problem (i.e., D2 to pure rotation, Cs to vibration-rotation, C3v and C(m) 3v to torsion-rotation). The meaning in this context of the traditional Ka, Kc labels for rotational energy levels in molecules with internal rotation is examined in detail. A discussion is also given of the relationship between three different schemes for defining a molecule-fixed axis system in internal rotation problems. i.e., the principal axis method, the internal axis method, and a hybrid method referred to here as the “rho axis method,” paying particular attention to the meaning of a-type, b-type, and c-type transitions when using each of these axis systems. Some of the above ideas were helpful in adding intensity calculations to our earlier computer program treating internal rotation and overall rotation in acetaldehyde-like molecules, and these intensity calculations are also briefly discussed. © 1994 Academic Press, Inc.
BibTeX:
@article{Hougen1994,
  author = {Hougen, J.T. and Kleiner, I. and Godefroid, M.},
  title = {Selection rules and intensity calculations for a cs asymmetric top molecule containing a methyl group internal rotor},
  journal = {Journal of Molecular Spectroscopy},
  year = {1994},
  volume = {163},
  pages = {559-586},
  doi = {10.1006/jmsp.1994.1047}
}
Abstract: Following slow collisions between O8+ and Ar, double-electron capture into 4l4l' and 4l5l' states of O6+ has been reported. The experimental results show that in 25% of the events the two electrons are retained on the oxygen presumably due to radiative stabilization. In order to understand this high rate of stabilization, we have calculated for the first time the decay properties of all the 4l4l' and 4l5l' terms in the isolated atom using a truncated diagonalization method with B-spline basis sets. The 4l4l' states are lying in the same range of energy as the higher members of the 3lnl' Rydberg series and we have extended our B-spline approach to represent accurately the 3lnl' states with n up to 50. In this static approach, we obtain 30.8% radiative stabilization for the 4l4l' manifold and 2.6% for the 4l5l' manifold assuming in both cases a statistical population of the states. We conclude that these values, when combined with the experimentally determined initial populations of the two configurations, are too small to explain the experimental features assuming a statistical population distribution and we propose that in order to clarify the situation an experimental and/or theoretical study of the population distribution over the two configurations is necessary. © 1994 IOP Publishing Ltd.
BibTeX:
@article{VanderHart1994,
  author = {Van der Hart, H.W. and Vaeck, N. and Hansen, J.},
  title = {Radiative stabilization in double-electron capture to 4l4l' and 4l5l' states in O6+},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1994},
  volume = {27},
  pages = {3489-3514},
  doi = {10.1088/0953-4075/27/15/023}
}
Abstract: In an attempt to refine our knowledge of the solar abundances of the CNO elements, we discuss in this paper the implications of a new accurate set of oscillator strengths recently calculated in intermediate coupling for the 2p(2Po)nl-2p(2Po)n′l′ E1 transitions of astrophysical interest in C I and also for the forbidden transitions within the 2p2 ground configuration. As with previous analyses devoted to nitrogen and oxygen, configuration interaction effects have been considered in the calculations in a detailed way and empirical adjustments have been introduced in the diagonal Hamiltonian matrix elements in order to improve the agreement between theoretical eigenvalues and experimental energy differences. The new LTE result, based on a sample of 55 E1 transitions observed in the visible and in the near infrared regions, is AC = 8.60 ± 0.03 in the usual logarithmic scale. Taking departures from LTE into account leads, for a sample of 31 weak lines, to a mean result AC = 8.57 ± 0.03 in agreement with recent determinations.
BibTeX:
@article{Biemont1993,
  author = {Biémont, E. and Hibbert, A. and Godefroid, M. and Vaeck, N.},
  title = {New f-values in C I and the CNO abundances in the sun},
  journal = {Astrophysical Journal},
  year = {1993},
  volume = {412},
  pages = {431-435}
}
Abstract: We present calculations of autoionization widths using a fully numerical multiconfigurational Hartree-Fock method (mchf). Energy positions and autoionization rates are given for several doubly-excited states lying below the n = 2 threshold in He [and H˜. Particular attention is given to orthogonality considerations in the computation of the autoionization widths. The method is extended to the ls2p2 2D, ls2s(3S)3d 2D and ls2s(3S)4d 2D states of Li 1. To the authors’ knowledge, our MCHF value, 12.5 meV, is the first result obtained for the autoionization width of the ls2s(3S)4d 2D state. Comparison is made with other theoretical results and with experimental values and we point out several inconsistencies between the two sets of results. © 1993 IOP Publishing Ltd.
BibTeX:
@article{Brage1993a,
  author = {Brage, I. and Fischer, C.F. and Vaeck, N.},
  title = {Mchf calculations of autoionization widths in two- and three-electron systems},
  journal = {Journal of Physics D: Applied Physics},
  year = {1993},
  volume = {26},
  pages = {621-640},
  doi = {10.1088/2015000624501X}
}
Abstract: We present calculations of autoionization widths using a fully numerical multiconfigurational Hartree-Fock method (mchf). Energy positions and autoionization rates are given for several doubly-excited states lying below the n = 2 threshold in He [and H-. Particular attention is given to orthogonality considerations in the computation of the autoionization widths. The method is extended to the ls2p2 2D, ls2s(3S)3d 2D and ls2s(3S)4d 2D states of Li 1. To the authors’ knowledge, our MCHF value, 12.5 meV, is the first result obtained for the autoionization width of the ls2s(3S)4d 2D state. Comparison is made with other theoretical results and with experimental values and we point out several inconsistencies between the two sets of results. © 1993 IOP Publishing Ltd.
BibTeX:
@article{Brage1993b,
  author = {Brage, I. and Fischer, C.F. and Vaeck, N.},
  title = {Mchf calculations of autoionization widths in two- and three-electron systems},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1993},
  volume = {26},
  pages = {621-640},
  doi = {10.1088/0953-4075/26/4/006}
}
Abstract: The effect of core polarization on binding energies, term splitting, fine structure, and transition probabilities is investigated for the low lying states 4s2S, 3d2D, 4p2P° in Ca II and 4s2‘S, 4s4p1'3P° in Ca I. Results from inclusions of core polarization in the form of model potentials are com­pared with explicit MCHF calculations, and the accuracy of the different approaches is discussed. © 1993 IOP Publishing Ltd.
BibTeX:
@article{Brage1993,
  author = {Brage, T. and Fischer, C.F. and Vaeck, N. and Godefroid, M. and Hibbert, A.},
  title = {Core polarization in ca i and ca ii},
  journal = {Physica Scripta},
  year = {1993},
  volume = {48},
  pages = {533-545},
  doi = {10.1088/0031-8949/48/5/006}
}
BibTeX:
@article{Bramley1993,
  author = {Bramley, M.J. and Henderson, J.R. and Tennyson, J. and Sutcliffe, B.T.},
  title = {On the Meyer-Botschwina-Burton potential energy surface for H 3+},
  journal = {The Journal of Chemical Physics},
  year = {1993},
  volume = {98},
  pages = {10104-10105}
}
Abstract: Non-adiabatic calculations on the positronium ion have been performed using laboratory-fixed hyperspherical coordinates and numerical wavefunctions. Convergence properties show that more than 98% of the true energy can be recovered using modest basis sets by truncating the radial domain and carrying out self-consistent field iterations solely on K = 0 levels. It seems likely that such procedures will enable more complex systems to be studied without recourse to extremely large basis sets. © 1993 Taylor & Francis Group, LLC.
BibTeX:
@article{Burden1993,
  author = {Burden, F.R. and Sutcliffe, B.T.},
  title = {Three-body calculations in laboratory-fixed hyperspherical coordinates: Convergence properties using numerical wavefunctions as applied to the positronium ion e-3},
  journal = {Molecular Physics},
  year = {1993},
  volume = {80},
  pages = {383-389},
  doi = {10.1080/00268979300102321}
}
Abstract: The angular distributions of electrons ejected from collisionally excited O- ions have been measured in order to test the previous assignments of excited states for this ion. The angular distributions support the interpretation that the two dominant peaks in the electron-energy spectrum represent the autodetachment of the 2p3(2D)3s2 2Do state, decaying to the 3P and 1D states of the oxygen ground-state configuration, with an experimental branching ratio of 1.58±0.08, and not that two different autodetaching states are populated, as previously assumed. Theoretical calculations are in good agreement with the experimental findings. © 1993 The American Physical Society.
BibTeX:
@article{Dahl1993,
  author = {Dahl, P. and Andersen, T. and Jodal, L. and Kylstra, N.J. and Hansen, J.E. and Vaeck, N.},
  title = {Angular distributions in autodetachment from doubly excited O- states},
  journal = {Physical Review A},
  year = {1993},
  volume = {48},
  pages = {2844-2849},
  doi = {10.1103/PhysRevA.48.2844}
}
Abstract: The energy of a level of a specific isotope is affected both by the nuclear motion and the nuclear volume. This program treats the resulting energy shift as a small perturbation that can be separated into the normal and specific mass shift and field shift. Given an electronic wave function, generated either by the MCHF program (LS format) or the MCHF_CI (LSJ format), isotope independent parameters are computed and, from these, shifts between isotopes are predicted. © 1993.
BibTeX:
@article{Fischer1993,
  author = {Fischer, C.F. and Smentek-Mielczarek, L. and Vaeck, N. and Miecznik, G.},
  title = {A program to compute isotope shifts in atomic spectra},
  journal = {Computer Physics Communications},
  year = {1993},
  volume = {74},
  pages = {415-431},
  doi = {10.1016/0010-4655(93)90023-6}
}
Abstract: The Fourier transform absorption spectrum of HONO was recorded at high resolution between 600 and 12 000 cm-1 using various experimental conditions. The results concerning the trans isomer are presented; i.e., the full rovibrational analysis of the ν1, ν2, ν3, ν4, and 2ν1 bands and the vibrational analysis and band contour simulation of the 2ν2, ν1 + ν4, ν1 + ν3, ν1 + 2ν3, and 3ν1 bands have been given. The results are combined with those of previous literature investigations to obtain a complete set of rovibrational parameters, including equilibrium rotational parameters, Ae = 3.122 cm-1, Be = 0.4230 cm-1, and Ce = 0.3724 cm-1. © 1993 Academic Press, Inc.
BibTeX:
@article{Guilmot1993,
  author = {Guilmot, J.-M. and Godefroid, M. and Herman, M.},
  title = {Rovibrational Parameters for trans-Nitrous Acid},
  journal = {Journal of molecular spectroscopy},
  year = {1993},
  volume = {160},
  pages = {387-400},
  doi = {10.1006/jmsp.1993.1186}
}
Abstract: We review some of the progress which has been achieved in calculations of atomic structure over the last few years, especially connected with the introduction of B-spline basis sets. The most important property of these basis sets is that they are effectively complete even in the case of a rather small set of basis functions. The possibilities for systematic calculations are discussed and applications to configuration interaction calculations as well as to calculations based on many-body perturbation theory are reviewed. © 1993 IOP Publishing Ltd.
BibTeX:
@article{Hansen1993,
  author = {Hansen, J.E. and Bentley, M. and Van Der Hart, H.W. and Landtman, M. and Lister, G.M.S. and Shen, Y.-T. and Vaeck, N.},
  title = {The introduction of b-spline basis sets in atomic structure calculations},
  journal = {Physica Scripta},
  year = {1993},
  volume = {1993},
  pages = {7-17},
  doi = {10.1088/0031-8949/1993/T47/001}
}
Abstract: The 3D discrete variable representation (DVR) calculations of Henderson and Tennyson [Chem. Phys. Lett. 173, 133 (1990)] are reanalyzed to find the source of the nonvariational behavior highlighted by Carter and Meyer [J. Chem. Phys. 96, 2424 (1992)]. The discrepancy is found to be caused not by the use of incorrect boundary conditions, but by a failure of the quadrature approximation commonly used hi DVR calculations. Corrected DVR calculations show variational but slow convergence. Calculations using the same intermediate vectors as the nonvariational calculations and a corrected final Hamiltonian show greatly enhanced convergence. The vibrational band origins computed with this method are converged to within 2 cm-1 up to 35 000 cm-1. A complete list of these is presented and comparisons made with previous predictions. © 1993 American Institute of Physics.
BibTeX:
@article{Henderson1993,
  author = {Henderson, J.R. and Tennyson, J. and Sutcliffe, B.T.},
  title = {All the bound vibrational states of H3 +: A reappraisal},
  journal = {The Journal of Chemical Physics},
  year = {1993},
  volume = {98},
  pages = {7191-7203}
}
Abstract: In his studies of f electrons in atoms, Racah introduced the group SO(7) and its subgroup G2, with irreducible representations (irreps) W and U. By using a quarklike basis, these groups can be conveniently embedded in SO(8). This larger group, with irreps V, possesses two other SO(7) groups as subgroups that themselves contain G2 as a common subgroup. One of them, SO(7)' (with irreps W'), has been used to derive new selection rules on operators of physical interest. We describe methods for calculating the overlaps (VWU mod VW' U), the ultimate aim being to facilitate the transformations between SO(7) and SO(7)'. A table of relevant 6-U symbols (the G2 generalizations of 6-j symbols) is given. When V possesses null triality (that is, when the symbols labelling the open ends of the Dynkin diagram for SO(8) are equal), an undetermined phase in the overlaps can be used to generate matrix representations of S3, the permutation group on three objects. A brief table of zero overlaps is given. A remarkable factorization of the overlaps ((4310)W(40) I(4310)W'(40)) is noted, where (4310) is the irrep of SO(8) with dimension 25725.
BibTeX:
@article{Judd1993,
  author = {Judd, B.R. and Lister, G.M.S. and Vaeck, N.},
  title = {Overlaps between the irreducible representations of two SO(7) subgroups of SO(8) used in the quark model of the atomic f shell},
  journal = {Journal of Physics A: Mathematical and General},
  year = {1993},
  volume = {26},
  article number = {028},
  pages = {4991-5005},
  doi = {10.1088/0305-4470/26/19/028}
}
Abstract: The excitation energies of the 3d4p 3Fo, 4s4f 3Fo, 3d4p 1Fo, and 4s4f 1Fo states relative to the ground state 4s2 1S and the ground-state ionization potential of neutral calcium (Ca i) are calculated using a finite-element multiconfiguration Hartree-Fock method, through the use of a systematic sequence of active spaces of increasing size. It is confirmed, through large-scale ab initio calculations, that a wrong position of the 3d4p perturber in the 1Fo series, found in valence multiconfiguration Hartree-Fock calculations, is due to the missing core-valence correlation. Some interference effects between core-valence and core-core correlation effects are also analyzed. © 1993 The American Physical Society.
BibTeX:
@article{Sundholm1993,
  author = {Sundholm, D. and Olsen, J. and Godefroid, M. and Van Meulebeke, G.},
  title = {Core-valence correlation on the low-lying 1,3Fo terms of Ca i},
  journal = {Physical Review A},
  year = {1993},
  volume = {48},
  pages = {3606-3610},
  doi = {10.1103/PhysRevA.48.3606}
}
Abstract: The usual quantum mechanical approach to the separation of electronic and nuclear motions is reformulated in a precise manner and re-examined. The coupling terms between the two kinds of motions prove to be rather elusive and their theoretical status often problematic. The problem areas are identified and suggestions are made about the ways in which the field might in future be developed. This Lennard-Jones memorial lecture was given on 21st September, 1992 at the Quantum Theory Conference in York.
BibTeX:
@article{Sutcliffe1993,
  author = {Sutcliffe, B.T.},
  title = {The coupling of nuclear and electronic motions in molecules},
  journal = {Journal of the Chemical Society, Faraday Transactions},
  year = {1993},
  volume = {89},
  pages = {2321-2335},
  doi = {10.1039/FT9938902321}
}
Abstract: In a recent tetter Bachau, Roncdn and Hare! have proposed an ingenious method based on the PCI effect to obtain stabilization of certain classes of autoionizing states during ion-atom collisions. In this comment we argue that although the effect as such is possible we find several difficulties with its application to cases for which stabilization has been observed. © 1993 IOP Publishing Ltd.
BibTeX:
@article{Vaeck1993,
  author = {Vaeck, N. and Hansen, J.E.},
  title = {Comment on ‘stabilization of autoionizing states during ion-atom collisions’},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1993},
  volume = {26},
  pages = {2977-2980},
  doi = {10.1088/0953-4075/26/17/028}
}
Abstract: This paper is the first part of a series devoted to the ab initio calculation of some vibrational properties helpful in the interpretation of high resolution spectroscopy, atmospherical and astrophysical data.An ab initio method of calculation of the vibrational transition energies and dipole moment matrix elements is described and analyzed.The main features of this method are the resolution of both electronic and vibrational problems by analytical variational techniques and the representation of the potential energy and dipole moment hypersurfaces as Taylor’s series expansions in normal coordinates up to the fourth order.The dipole moment matrix elements are then evaluated by simple analytical formulae.In this first paper, some of the approximations inherent to the methodology are systematically analyzed on the basis of results obtained for diatomic molecules (BeH, HF, NH and NO) with a comparison to experimental and other theoretical results found in the literature.The dependence on the results of the effects of electrical and mechanical anharmonicities, electron correlation and basis set dependencies are investigated.The applicability of the method to small polyatomic systems is discussed in the second paper of this series, on the basis of test calculations on the water molecule. © 1992 IOP Publishing Ltd.
BibTeX:
@article{Cantarella1992,
  author = {Cantarella, E. and Culott, F. and Lievin, J.},
  title = {Ab initio calculation of vibrational dipole moment matrix elements.I.methods of calculation and diatomic test systems},
  journal = {Physica Scripta},
  year = {1992},
  volume = {46},
  pages = {489-501},
  doi = {10.1088/0031-8949/46/6/003}
}
Abstract: This paper is the second part of a series devoted to the ab initio calculation of vibrational properties, like transition energies, dipole moment matrix elements and infrared intensities.The method of calculation has been detailed in the first paper, where test calculations on diatomic systems were also analyzed.The present paper applies the method to a simple polyatomic system, the water molecule in its ground electronic state.The purely polyatomic features of the method are discussed, as the determination of the potential energy and dipole moment surfaces and the description of vibrational mode couplings.The results concern vibrational energies of levels in the range 0 < v1+ v2+ v3< 3 and vibrational transition moments and intensities of cold and hot bands.Many methodological tests and comparisons to the experimental and theoretical literature are reported, showing that theoretical values of transition energies and dipole moments converge to the experimental ones; at the highest level of approximation (TZ + 2P/SD-CI; vibrational SCF/CI and FCI) the precision obtained is sufficient to provide useful complementary spectroscopical data.This convergence is however not achieved for diagonal dipole moment matrix elements, which are shown to be very sensitive to the mechanical and electrical anharmonicities. © 1992 IOP Publishing Ltd.
BibTeX:
@article{Culot1992,
  author = {Culot, F. and Lievin, J.},
  title = {Ab initio calculation of vibrational dipole moment matrix elements.Ii.the water molecule as a polyatomic test case},
  journal = {Physica Scripta},
  year = {1992},
  volume = {46},
  pages = {502-517},
  doi = {10.1088/0031-8949/46/6/004}
}
Abstract: Calculations of KLL and LMM transition energies and autoionisation transition probabilities for KLL transitions are reported for nitrogen ions with different L-shell populations. These quantities are of interest for the understanding of the process of neutralisation of ions at surfaces. A number of experiments have been carried out recently in which KLL and LMM Auger electrons have been observed. The observed energies have been used to obtain information about the number of L (M) electrons present when the KLL (LMM) transitions occur and about the population of the outer shells at this point. The spread in the quantities we report show that only very limited conclusions can be drawn from the observed energies about these two aspects of the neutralisation process. © 1992 IOP Publishing Ltd.
BibTeX:
@article{Hansen1992,
  author = {Hansen, J.E. and Schraa, O. and Vaeck, N.},
  title = {Calculations of auger energies and autoionisation rates for KLL and LMM transitions involved in the neutralisation of nitrogen ions at surfaces},
  journal = {Physica Scripta},
  year = {1992},
  volume = {1992},
  pages = {41-44},
  doi = {10.1088/0031-8949/1992/T41/007}
}
BibTeX:
@article{Henderson1992,
  author = {Henderson, J.R. and Tennyson, J. and Sutcliffe, B.T.},
  title = {Reply to Comment on: Discrepancies between variationally calculated vibrational energies of H3 +},
  journal = {Journal of Chemical Physics},
  year = {1992},
  volume = {96},
  pages = {2426-2427},
  doi = {10.1063/1.462045}
}
Abstract: We have fitted to within experimental accuracy a data set for acetaldehyde consisting of 423 vt = 0 microwave lines, 270 vt = 1 microwave lines, and 214 vt = 1 ← 0 far-infrared lines, using a global model from the earlier literature. The vt = 1 microwave data set was extended and corrected by 76 new measurements from NIST; the theoretical model was extended by inclusion of higher order terms from the literature. The final fit requires only 34 parameters to achieve a unitless weighted standard deviation for the whole fit of 1.15, demonstrating both the power of the model and the internal consistency of the data. © 1992.
BibTeX:
@article{Kleiner1992,
  author = {Kleiner, I. and Hougen, J.T. and Suenram, R.D. and Lovas, F.J. and Godefroid, M.},
  title = {The ground and first torsional states of acetaldehyde},
  journal = {Journal of Molecular Spectroscopy},
  year = {1992},
  volume = {153},
  pages = {578-586},
  doi = {10.1016/0022-2852(92)90494-9}
}
Abstract: Ab initio calculations on the few lowest 1Ag states of trans-bent acetylene have been performed at different levels of theory (SCF, CASSCF, SD-CI, and SO-CI) and with basis sets of increasing flexibilities (3-21G + pol, TZ + 2P, TZ + 2P + diff). The results predict the existence of an equilibrium structure (RCC = 1.621 A ̊, RCH = 1.096 A ̊, and θHCC = 104.5°) on the second potential energy surface of 1Ag symmetry, corresponding to the valence configuration 1ag21bu22ag22bu23ag23bu 24ag2 arising from a double Π → Π* excitation applied to the ground state configuration. The calculated parameters for this state, labeled C ̃′ (A = 8.71, B = 0.912, C = 0.825 cm-1; ν1 = 3126, ν2 = 934, ν3 = 1386 cm-1; Te = 7.53 eV), strictly confirm the recent findings of UVODR experiments. The analysis of the wavefunctions allows an interpretation of some of the features of this state, namely, its valence nature, its geometry (strong bending and enlarged CC bond), and the occurrence of multiple avoided crossings, leading to a potential energy barrier, along the pathway linking the C ̃′ minimum to the linear ground state geometry. The reason why previous ab initio calculations did not report the existence of this state is also discussed. © 1992.
BibTeX:
@article{Lievin1992,
  author = {Lievin, J.},
  title = {Ab initio characterization of the C ̃′1Ag state of the acetylene molecule},
  journal = {Journal of Molecular Spectroscopy},
  year = {1992},
  volume = {156},
  pages = {123-146},
  doi = {10.1016/0022-2852(92)90098-9}
}
Abstract: It is shown that vibrational band intensities calculated using variational wavefunctions and dipole surfaces give results which depend on how the Cartesian axes of the dipole surface are defined. It is suggested that the most consistent definition of these axes uses the rules proposed by Eckart for separating rovibrational motion. The consequences of this choice of axis system for the calculated band intensities of H2S, LiNC and H3+, and the apparent validity of Hönl-London factors are discussed. Computed band intensities are presented for H2S, HDS and D2S which correct previous literature values. © 1992 Taylor and Francis Group, LLC.
BibTeX:
@article{RuthLeSueur1992,
  author = {Ruth Le Sueur, C. and Miller, S. and Tennyson, J. and Sutcliffe, B.T.},
  title = {On the use of variational wavefunctions in calculating vibrational band intensities},
  journal = {Molecular Physics},
  year = {1992},
  volume = {76},
  pages = {1147-1156},
  doi = {10.1080/00268979200101941}
}
Abstract: Since Coulson's Tilden Lecture in 1951 there have been many developments in ideas about the chemical bond and about molecular structure. One aspect of those developments is considered here from a quantum mechanical standpoint. The conclusion reached is one of qualified pessimism about the extent to which it is possible to account for bonding and molecular structure (as perceived by the working chemist) from a quantum mechanical point of view. © 1992.
BibTeX:
@article{Sutcliffe1992a,
  author = {Sutcliffe, B.T.},
  title = {The chemical bond and molecular structure},
  journal = {Journal of Molecular Structure: THEOCHEM},
  year = {1992},
  volume = {259},
  pages = {29-58},
  doi = {10.1016/0166-1280(92)87004-J}
}
Abstract: That part of the vibration-rotation Hamiltonian for a triatomic molecule which is independent of the rotational motion, is expressed in generalized distance and generalized perimetric coordinates which, in special cases, are the interparticle coordinates and the standard perimetric coordinates. © 1992 Taylor & Francis Ltd.
BibTeX:
@article{Sutcliffe1992b,
  author = {Sutcliffe, B.T.},
  title = {The use of perimetric coordinates in the vibration-rotation hamiltonian for triatomic molecules},
  journal = {Molecular Physics},
  year = {1992},
  volume = {75},
  pages = {1233-1236},
  doi = {10.1080/00268979200100941}
}
BibTeX:
@article{Sutcliffe1992,
  author = {Sutcliffe, B.T. and Smith, S.J. and Duffey, G.H.},
  title = {Computing the tetrahedral angle [3] (multiple letters)},
  journal = {Journal of Chemical Education},
  year = {1992},
  volume = {69},
  pages = {171}
}
Abstract: A previously proposed [Sutcliffe and Tennyson, Int. J. Quantum Chem. 29, 183 (1991)] body‐fixed Hamiltonian is applied to AB2 systems in Radau coordinates with the x‐axis embedded along the bisector of the angle. It is shown that by using a discrete variable representation for the angular coordinate it is possible to avoid singular regions of the Hamiltonian. A two‐step variational procedure is used to obtain rotationally excited states of the system. The results of test calculations H2S and D2S with J = 0, 1, 5, and 10 are discussed along with computer‐usage characteristics. Copyright © 1992 John Wiley & Sons, Inc.
BibTeX:
@article{Tennyson1992,
  author = {Tennyson, J. and Sutcliffe, B.T.},
  title = {Dicretization to avoid singularities in vibration–rotation Hamiltonians: A bisector embedding for AB2 triatomics},
  journal = {International Journal of Quantum Chemistry},
  year = {1992},
  volume = {42},
  pages = {941-952},
  doi = {10.1002/qua.560420429}
}
Abstract: Elaborate multiconfiguration Hartree-Fock wave functions have been obtained for the 4s 2S, 3d 2D, and 4p 2P°states in Ca+ in order to investigate the core-valence correlation effects on the transition probabilities of the electric dipole (E1) and quadrupole (E2) processes involving these levels. In parallel, model-potential calculations using a core-polarization potential have been performed. They support the large reduction of the oscillator strengths found in the ab initio approach for both the E1 and E2 processes. The agreement between the two sets of results is satisfactory only if the polarization term is included in the Hartree-Fock variational procedure. The present theoretical 2P°1/2,3/2 lifetime values differ by 3.5% from the most recent fast-beam laser measurements with an estimated single-standard-deviation uncertainty of about 1%. © 1992 The American Physical Society.
BibTeX:
@article{Vaeck1992d,
  author = {Vaeck, N. and Godefroid, M. and Froese Fischer, C.},
  title = {Core-valence correlation effects on E1 and E2 decay rates in Ca+},
  journal = {Physical Review A},
  year = {1992},
  volume = {46},
  pages = {3704-3716},
  doi = {10.1103/PhysRevA.46.3704}
}
Abstract: We present results of calculations of decay rates for hollow atoms which could be formed when an ion approaches a surface and we discuss the implications of these results for the interpretation of recent experiements concerned with the neutralisation of slow highly charged ions at surfaces. We find that multiply excited states in neutral atoms have lifetimes considerably shorter than those in the corresponding ions and point out that this property can explain the large number of low-energy electrons, which have been observed experimentally. In addition, the lifetimes appear to be of the right order of magnitude to explain the observed time development of the neutralisation process. We consider also the implications for the high-energy spectrum. © 1992.
BibTeX:
@article{Vaeck1992b,
  author = {Vaeck, N. and Hansen, J.E.},
  title = {Auger decay of slow highly-ionised ions neutralised at surfaces},
  journal = {Surface Science},
  year = {1992},
  volume = {269-270},
  pages = {596-600},
  doi = {10.1016/0039-6028(92)91316-4}
}
Abstract: We consider the probability for double-Auger decay of multiply-excited states in Nn+ with two Is vacancies. We have calculated the branching ratio R3 between the double-Auger decay filling both holes in the Is shell and the normal Auger decay for initial 2pN, 2s2pN-l and 2s22pN-2 configurations with N = 3, 4, 5 and 6. We show that R3 depends more strongly on the number of 2s electrons than on the total number of electrons in the n = 2 shells. We find that the ‘shake-down’ of a 2s electron due to the non-orthogonality between the initial 2s and the final is electron is the most important effect. Comparison with the result of recent studies of neutralization of slow highly-excited ions at surfaces suggests the presence of one or two 2s electrons in the ion at the time of the double-Auger decay. © 1992 IOP Publishing Ltd.
BibTeX:
@article{Vaeck1992,
  author = {Vaeck, N. and Hansen, J.E.},
  title = {Calculations of autoionization rates for double-auger decay of multiply-excited states in nitrogen},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1992},
  volume = {25},
  pages = {3613-3619},
  doi = {10.1088/0953-4075/25/17/013}
}
Abstract: We report calculations of energies and decay rates for triply-excited 3l3l’3l” configurations in Li-like N, N4+, and in B-like N, N2+, using a configuration interaction approach. Triply-excited configurations can be obtained in charge-exchange experiments and might be important in the process of neutralization of slow highly-ionized ions at surfaces but nearly no spectroscopic information is available for such states. They have found that there is a very strong configuration mixing in these systems which makes it difficult to give single-particle labels to the terms. This suggests that a molecular (collective) description might be useful in analogy with the molecular model of the doubly-excited nlnl’ configurations in He-like spectra. Watanabe and Lin (1987) have considered a molecular description of the 3l3l’3l” configurations in He−. We have considered whether this model is useful in the present case where the nuclear attraction is much stronger compared to the interelectronic repulsion but they do not find any compelling evidence for such a description. One of the motivations for the introduction of the collective model in the case of the doubly-excited states was the large difference between non-radiative decay rates for different states in these systems. However, we have not found evidence from the decay rates in the 3131’31” configurations far a collective behaviour of the atomic shell. The 3131’31” configurations have many levels and can be difficult to resolve experimentally so average values are often more useful for comparison with experiment than rates for individual levels. We show that the average values of the decay rates, calculated assuming that there is no configuration interaction between the 3131’31” configurations, are in very good agreement with the correct average values even though configuration interaction is very strong. Since doublyexcited states of the type 3131’ have a rather long lifetime we have suggested that multiply-excited states might be formed in the neutralization of slow highly-ionized ions at surfaces. We have found that triply-excited states have a considerably shorter lifetime and if additional electrons are added the lifetime seems to be reduced further so that this type of configuration can be responsible for the large number of low-energy electrons which are produced during a neutralization process. © 1992 IOP Publishing Ltd.
BibTeX:
@article{Vaeck1992c,
  author = {Vaeck, N. and Hansen, J.E.},
  title = {Calculations of Energies, Radiative and Non-Radiative Decay Rates of Triply-Excited States in Li-Like and B-Like Nitrogen},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1992},
  volume = {25},
  pages = {883-905},
  doi = {10.1088/0953-4075/25/5/005}
}
Abstract: Results are presented for radiative and non-radiative decay rates for 3l3l′ nlʺ states in N4+and 2lnlʹ states in N5+in a single configuration as well as in a CI approximation. It is found that while radiative stabilization is negligible for the triply-excited states it is important for the doubly-excited states with n > 6. These results are used to interpret multiple charge-exchange experiments in nitrogen by Benoit-Cattin et al. The reasons for the difference between the doubly-and triply-excited states are discussed. © 1992 IOP Publication Ltd.
BibTeX:
@article{Vaeck1992a,
  author = {Vaeck, N. and Hansen, J.E.},
  title = {Competition between radiative and non-radiative decay processes in triply-excited 3l3l′ nlʺ and doubly-excited 2 lnl′ states in nitrogen ions},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1992},
  volume = {25},
  pages = {3267-3282},
  doi = {10.1088/0953-4075/25/15/009}
}
Abstract: Theoretical and experimental isotope shifts for Ca l and Sr i levels are presented. The isotope shifts of the levels 4s6s1S0 4p2 ‘So and 4p21D2 of calcium have been measured between the isotopes 40, 42, 43, 44 and 48 in two-photon transitions from the Ca ground state using two lasers with different wavelengths. Results of ab inilio mass and field shift calculations are presented for these levels as well as for a number of other strongly perturbed low-lying levels in calcium and strontium using the multiconfigutation Hartree-Fock method. The ‘gradient’ and the alternative ‘Slater’ forms of the specific mass shift operator have been tested; the latter is found to be unreliable with our mchf expansions which are limited to valence correlation effects. The agreement between theory and experiment is systematically better in strontium than in calcium for the specific mass shifts. The ab inilio field shift values agree well with the trend of the observations for both atoms, although they are systematically too small. A semiempirical calibration procedure leads to very good agreement for both atoms. Core-relaxation effects are shown to be large particularly for the mass shift. © 1991 IOP Publishing Ltd.
BibTeX:
@article{Aspectt1991,
  author = {Aspectt, A. and Bauchei, J. and Godefroid, M. and Grangier, P. and Hansen, J.E. and Vaeck, N.},
  title = {Experimental and mchf isotope shifts of strongly perturbed levels in ca i and sr i},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1991},
  volume = {24},
  pages = {4077-4099},
  doi = {10.1088/0953-4075/24/18/019}
}
Abstract: Knowledge of accurate oscillator strengths in neutral oxygen is of crucial importance in astrophysics. The accurate determination of the solar abundance of O I, which remains the primary source for the entry in cosmic abundance tables, requires the use of E1 transitions appearing in the solar photospheric spectrum. A new accurate scale of oscillator strengths has therefore been obtained for the 2p3(4S)nl-2p3(4S)n′l′ transitions of O I of astrophysical interest. Configuration interaction effects have been considered in a detailed way. The results have been used to improve the solar abundance determination for oxygen. The new result is A(O) = 8.86 ± 0.04 (in the usual logarithmic scale).
BibTeX:
@article{Biemont1991,
  author = {Biémont, E. and Hibbert, A. and Godefroid, M. and Vaeck, N. and Fawcett, B.C.},
  title = {Accurate oscillator strengths of astrophysical interest for neutral oxygen},
  journal = {Astrophysical Journal},
  year = {1991},
  volume = {375},
  pages = {818-822}
}
Abstract: Given wave-function expansions for the initial and final state along with expressions for the transition matrix elements, the programs evaluate oscillator strengths and transition probabilities. The MCHF_LSTR program assumes wave functions are represented in the non-relativistic formalism and computers E1 and E2 transition data. The MCHF_LSJTR program requires wave-function expansions from a Breit-Pauli CI calculation and evaluates transition data for E1, E2, ..., or M1, M2, ..., transitions between a series of initial and final states. This program could be used for the study of transitions between multiplets. © 1991.
BibTeX:
@article{FroeseFischer1991,
  author = {Froese Fischer, C. and Godefroid, M.R.},
  title = {Programs for computing LS and LSJ transitions from MCHF wave functions},
  journal = {Computer Physics Communications},
  year = {1991},
  volume = {64},
  pages = {501-519},
  doi = {10.1016/0010-4655(91)90141-7}
}
Abstract: The MCHF_MLTPOL program performs the angular integrations necessary for expressing the matrix elements of transition operators, E1, E2, ..., or M1, M2, ..., as linear combinations of radial integrals. All matrix elements for transitions between two lists of configuration states will be evaluated. A limited amount of non-orthogonality is allowed between orbitals of the initial and final state. © 1991.
BibTeX:
@article{FroeseFischer1991a,
  author = {Froese Fischer, C. and Godefroid, M.R. and Hibbert, A.},
  title = {A program for performing angular integrations for transition operators},
  journal = {Computer Physics Communications},
  year = {1991},
  volume = {64},
  pages = {486-500},
  doi = {10.1016/0010-4655(91)90140-G}
}
Abstract: The autoionizing spectrum of Ca has been studied in the wavelength ranges of 490-540 nm and 555-590 nm through multiphoton absorption and the subsequent decay to excited Ca+(4p2P3/2, 1/2) states. The fluorescence signal of Ca+(4p) exhibits resonances attributed to the 3d6p and 3dnf (n=4-7) doubly excited autoionizing 3 = 1, 3 states (three-photon absorption) together with resonances due to excited bound states (two- photon absorption) of the neutral atom. Sufficient atomic density was obtained utilizing a vapour in a moderate pressure regime (2-5 mTorr) such that collisional excitation was stilt negligible. The pulsed  -8 ns duration (fwhm) laser radiation was used in linear as well as in circular polarization. The observed 3 = 3 states has been interpreted with the help of theoretical results obtained by a configuration interaction approach. © 1991 IOP Publishing Ltd.
BibTeX:
@article{Gaardsted1991,
  author = {Gaardsted, J.O. and Andersent, T. and Haugen, H.K. and Hansen, J.E. and Vaeck, N.},
  title = {Multiphoton spectroscopy of doubly excited autoionizing states of ca},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1991},
  volume = {24},
  pages = {4363-4377},
  doi = {10.1088/0953-4075/24/20/008}
}
Abstract: The singly excited functions satisfying Brillouin theorem are expressed as linear combinations of configuration‐state functions for any spin and spatial symmetries (atomic or molecular) and for any reference wave function. The generality of the formulation is ensured by the use of the irreducible tensor method that can be adapted to any symmetry point group of interest. The expansion coefficients are simply written as products of fractional parentage coefficients, spin‐ and orbit‐recoupling coefficients, and phase factors. The formalism is illustrated for some atomic (Kh) and molecular (C∞v, C3v, and Td) configurations. Group theoretical techniques are also used to correlate the Brillouin conditions within a chain of groups. Copyright © 1991 John Wiley & Sons, Inc.
BibTeX:
@article{Godefroid1991,
  author = {Godefroid, M. and Lievin, J. and Metz, J.‐Y.},
  title = {Symmetry adapted formulation of the generalized Brillouin theorem},
  journal = {International Journal of Quantum Chemistry},
  year = {1991},
  volume = {40},
  pages = {243-264},
  doi = {10.1002/qua.560400207}
}
Abstract: Recent calculations of doubly-excited states for two and four-electron states in neutral atoms and ions are described. In particular the radiative properties of these states are considered. It is pointed out that some of these states live so long that triply-excited states perhaps can be formed in neutralisation processes at surfaces. © 1991 Springer-Verlag.
BibTeX:
@article{Hansen1991,
  author = {Hansen, J.E. and van der Hart, H. and Landtman, M. and Shen, Y.-T. and Vaeck, N.},
  title = {Calculations for doubly-excited states populated in two-electron processes},
  journal = {Zeitschrift für Physik D Atoms, Molecules and Clusters},
  year = {1991},
  volume = {21},
  pages = {S87-S91},
  doi = {10.1007/BF01426256}
}
Abstract: Atomic transition rates and f values have been calculated in the triplet and quintet systems and for some intercombination lines of neutral oxygen. Configuration interaction was included in tbs calculations performed with the CiV3 code of Hibbcrt for all the transitions connecting the n =3 and n =4 energy levels. In order to reproduce the observed energy splittings between the energy states, small empirical adjustments were introduced to the diagonal matrix elements. Comparisons with previously published f values and radiative lifetimes are discussed and the subsequent astrophysical applications of the results are briefly mentioned. © 1991 IOP Publishing Ltd.
BibTeX:
@article{Hibbertt1991,
  author = {Hibbertt, A. and Biémont, E. and Godefroid, M. and Vaeck, N.},
  title = {El transitions of astrophysical interest in neutral oxygen},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1991},
  volume = {24},
  pages = {3943-3958},
  doi = {10.1088/0953-4075/24/18/010}
}
Abstract: New microwave measurements on the ground state of acetaldehyde have been carried out using a Fourier transform spectrometer in the region from 7 to 26 GHz (typical measurement uncertainty 4 kHz), and a conventional Stark spectrometer in the region from 45 to 116 GHz (typical measurement uncertainty 40 kHz). These new ground state measurements and remeasurements have permitted a much better fit to two theoretical models of a data set containing far-infrared combination differences from the literature, microwave transitions from the literature, and the new microwave transitions. Root-mean-square residuals obtained here for all these data (which come from a large number of sources) are only slightly larger (for either model) than the estimated measurement uncertainties. The first theoretical model is essentially a high-barrier effective Hamiltonian for one vibrational state only, based on Fourier expansions in terms of the form cos( 2πn 3)(ρK - σ). The second model is based on calculation using the internal-rotation potential function, and is in principle much more powerful than the first. The present successful fits using either model indicate that earlier fitting difficulties using the second model and a combined infrared and microwave data set were caused by problems in the microwave data set, rather than problems in the model. It is hoped that similar success can be achieved with the more powerful second model when data from higher excited torsional states are considered. © 1991.
BibTeX:
@article{Kleiner1991,
  author = {Kleiner, I. and Hougen, J.T. and Suenram, R.D. and Lovas, F.J. and Godefroid, M.},
  title = {The ground torsional state of acetaldehyde},
  journal = {Journal of Molecular Spectroscopy},
  year = {1991},
  volume = {148},
  pages = {38-49},
  doi = {10.1016/0022-2852(91)90032-6}
}
Abstract: The 0-0 band of the a ̃3Au- X ̃1Ag system of trans-glyoxal has been recorded in absorption using a Bomem DA3.002 Fourier-transform spectrometer. Rotational analysis reveals that the dominant structure consists of branches obeying the selection rules ΔJ = 0, ±1, ΔN = 0, ±1, ±2, and ΔKa = 0. The following molecular constants were obtained for the excited state (in cm-1): A = 1.9681(7), B = 0.15699(3), C = 0.14543(4), a0 = 0.025(3), a = -0.008(3), α = -0.08(3), T0 = 19 198.63(2), where the error limits are 3σ. © 1991.
BibTeX:
@article{Ramsay1991,
  author = {Ramsay, D.A. and Vervloet, M. and Vanhorenbeke, F. and Godefroid, M. and Herman, M.},
  title = {Rotational analysis of the 0-0 band of the a ̃3Au- X ̃1Ag system of trans-glyoxal},
  journal = {Journal of Molecular Spectroscopy},
  year = {1991},
  volume = {149},
  pages = {348-355},
  doi = {10.1016/0022-2852(91)90291-H}
}
Abstract: An exact, within the Born–Oppenheimer approximation, body‐fixed Hamiltonian for the nuclear motions of a triatomic system is presented. This Hamiltonian is expressed in terms of two arbitrarily defined internal distances and the angle between them. The body‐fixed axis system is related to these coordinates in a general fashion. Problems with singularities and the domain of the Hamiltonian are discussed using specific examples of axis embedding. A number of commonly used coordinate systems including Jacobi, bond‐length‐bond‐angle, and Radau coordinates are special cases of this Hamiltonian. Sample calculations on the H2S molecule are presented using all these and other coordinate systems. The possibility of using this Hamiltonian for reactive scattering calculations is also discussed. Copyright © 1991 John Wiley & Sons, Inc.
BibTeX:
@article{Sutcliffe1991,
  author = {Sutcliffe, B.T. and Tennyson, J.},
  title = {A general treatment of vibration‐rotation coordinates for triatomic molecules},
  journal = {International Journal of Quantum Chemistry},
  year = {1991},
  volume = {39},
  pages = {183-196},
  doi = {10.1002/qua.560390208}
}
Abstract: We report extensive multiconfiguration Hartree-Fock (MCHF) calculations, taking into account valence correlation and core-relaxation effects, of energy levels, eigenvector compositions, electric dipole and quadrupole oscillator strengths involving the n*S (n = 1-4), n1P° (n = 1, 2), n1D (n = 1—3) and n1F° (n = 1, 2) states in Ca I. On the whole, the agreement between theory and observation has been improved by our set of MCHF results. The theoretical transition probabilities allow the evaluation of the lifetimes for the levels 4s4p, 4s5p IP°; 4s4d, 4p2 *D and 3d4p, 4s4f 1F° which are compared with the most recent measurements. The differences between MCHF calculations for series perturbed by doubly-exdted states in Ca and Sr are discussed. It is concluded that core-polarization effects are of about the same importance in the two atoms but that the effects on the 3d (Ca) and 4d (Sr) orbitals are such that the total core-polarization effects for series and perturbers are of the same magnitude in Sr while large differences exist in Ca. © 1991 IOP Publishing Ltd.
BibTeX:
@article{Vaeck1991b,
  author = {Vaeck, N. and Godefroid, M. and Hansen, J.E.},
  title = {Mchf oscillator strength and lifetime calculations in neutral calcium},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1991},
  volume = {24},
  pages = {361-381},
  doi = {10.1088/0953-4075/24/2/006}
}
Abstract: We report here calculations of energy level values and autoionization decay rates for all the terms belonging to the 1s23 l3 l'3 l'' configuration in N2+. Comparison are made with previous calculations for 1s23 l3 l' terms in N3+. The properties of the triply-excited states and in particular the fast autoionization decay rates found in the present calculations can perhaps help in understanding the mechanism responsible for neutralisation of ions at surfaces. © 1991 Springer-Verlag.
BibTeX:
@article{Vaeck1991,
  author = {Vaeck, N. and Hansen, J.E.},
  title = {Calculations of decay rates for triply-excited states in N2+},
  journal = {Zeitschrift für Physik D Atoms, Molecules and Clusters},
  year = {1991},
  volume = {21},
  pages = {S221-S223},
  doi = {10.1007/BF01426298}
}
Abstract: It has been observed experimentally that slow highly-ionized atoms are already neutralized on impact with a metal surface due to the strong potential which can 'puli’ electrons out of the surface into high-lying multiply-excited atomic states. We present quantitative results for decay rates of such multiply-excited states and show that the lifetimes for such states, when the electrons have large values of n, appear to be significantly different in neutral atoms and in the corresponding ions. © 1991 IOP Publishing Ltd.
BibTeX:
@article{Vaeck1991a,
  author = {Vaeck, N. and Hansen, J.E.},
  title = {Lifetimes of multiply-excited states in nitrogen},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1991},
  volume = {24},
  pages = {L469-L475},
  doi = {10.1088/0953-4075/24/19/001}
}
Abstract: The spectrum of trans-nitrous acid has been recorded at a resolution of about 2.5 × 10-3 cm-1 in the region from 3200 to 3800 cm-1. Over 500 lines are assigned to the ν1 fundamental band (OH stretching). Rovibrational constants are obtained for ν1. Systematic perturbations affecting some of the levels are attributed to a b-type Coriolis interaction involving the 2ν3 + ν5 + ν6 level. © 1990.
BibTeX:
@article{Guilmot1990,
  author = {Guilmot, J.M. and Carleer, M. and Godefroid, M. and Herman, M.},
  title = {The ν1 fundamental band of trans-HNO2},
  journal = {Journal of Molecular Spectroscopy},
  year = {1990},
  volume = {143},
  pages = {81-90},
  doi = {10.1016/0022-2852(90)90262-O}
}
Abstract: The geometrical parameters concerning acetylene in the A ̃ state are derived: rCC = 1.375 A ̊, rCH = 1.097 A ̊, and HCH = 122.48°. New rovibrational parameters of acetylene in the A ̃ state are provided or predicted. Axis-switching intensities are discussed on the basis of an extended formulation using the tensor algebra. © 1990.
BibTeX:
@article{Huet1990,
  author = {Huet, T.R. and Godefroid, M. and Herman, M.},
  title = {The A ̃ electronic state of acetylene: Geometry and axis-switching effects},
  journal = {Journal of Molecular Spectroscopy},
  year = {1990},
  volume = {144},
  pages = {32-44},
  doi = {10.1016/0022-2852(90)90306-B}
}
Abstract: High-resolution spectroscopy and low-temperature experimental conditions allowed us to carry out the rotational analysis of the ν15 fundamental band of acetaldehyde, observed around 150 cm-1. Some 1000 lines of A and E types have been assigned to the main band and some 90 A-type lines have been identified in the first overtone of the torsion mode. A simultaneous fit, using the nonrigid internal axis method, of a very severely selected set of unblended FIR data from the fundamental band (214 lines with J ≤ 10 and K <- 9), together with microwave data published in the literature, allowed us to obtain accurate molecular parameters describing describing internal and overall rotation in acetaldehyde. In particular, the Fourier coefficients V3 and V6 of the barrier for internal rotation as well as the rotationless origins of the ν15 fundamental band and its first overtone were determined with improved accuracy, compared to the data previously available in the literature. Some difficulties in treating vt = 1 microwave data led us to suspect problems in the theoretical model adopted or in the present vt = 1 microwave data set. Finally, a fit of selected unblended data from the first overtone of the torsion (29 A-type lines), together with the previously mentioned selected unblended data from the fundamental band, was carried out but resulted in a standard deviation somewhat higher than was obtained with the fundamental band alone. © 1990.
BibTeX:
@article{Kleiner1990,
  author = {Kleiner, I. and Godefroid, M. and Herman, M. and McKellar, A.R.W.},
  title = {The fundamental torsion band in acetaldehyde},
  journal = {Journal of Molecular Spectroscopy},
  year = {1990},
  volume = {142},
  pages = {238-253},
  doi = {10.1016/0022-2852(90)90181-O}
}
Abstract: Calculations of the linestrengths and transition frequencies of the forbidden pure rotational spectrum of H3+ in the vibrationally excited ν2 state are presented. These transitions occur in the far-infrared region, and their observation may be complicated by ν1 - ν2 difference transitions. Examples of these are also given. Forbidden rovibrational transition frequencies and linestrengths have also been calculated in the frequency range 2000-3000 cm-1. The bands (ν2 + ν1) - ν2 and (2ν2 (l = 0) + ν1) - 2ν2 (l = 2) are found to be particularly strong. Possible phenomenological explanations for the observed line intensities are discussed. Two routes to obtaining the energy levels of the ν1 manifold of H3+ are suggested. © 1990.
BibTeX:
@article{Miller1990,
  author = {Miller, S. and Tennyson, J. and Sutcliffe, B.T.},
  title = {Forbidden rotational and rovibrational transitions in H3+: First principles calculations},
  journal = {Journal of Molecular Spectroscopy},
  year = {1990},
  volume = {141},
  pages = {104-117},
  doi = {10.1016/0022-2852(90)90281-T}
}
BibTeX:
@article{Verhaegen1990,
  author = {Verhaegen, G.},
  title = {50 years of A.M.U.B. (Association of Physicians graduated from the Free University of Brussels) [Pour les cinquante ans de l'A.M.U.B.]},
  journal = {Revue Medicale de Bruxelles},
  year = {1990},
  volume = {11},
  pages = {328-329}
}
Abstract: Benchmark first principles calculations of the pure rotational and ro-vibrational transition frequencies and line strengths are presented, using two independent program suites. Both sets of calculations were performed using the same potential energy and dipole surfaces. Our example calculations use recently calculated surfaces for H2S which have been shown to give good agreement with experimental data. The results, which show perfect agreement for the energy levels, transition frequencies and line strengths, are used as an external check on the two program suites. It is suggested they could provide a standard with which other groups working in this field can compare their calculations. © 1989.
BibTeX:
@article{Carter1989,
  author = {Carter, S. and Rosmus, P. and Handy, N.C. and Miller, S. and Tennyson, J. and Sutcliffe, B.T.},
  title = {Benchmark calculations of first principles rotational and ro-vibrational line strenghts},
  journal = {Computer Physics Communications},
  year = {1989},
  volume = {55},
  pages = {71-75},
  doi = {10.1016/0010-4655(89)90064-7}
}
Abstract: A new method to discretise the Schrodinger equations has been described recently and applied successfully to simple quantum mechanical and nuclear Hartree-Fock problems. The method is based on an accurate approximation of a variational calculation. The authors apply this approach in atomic structure calculations by discretising on Laguerre meshes the Schrodinger equation for hydrogen and the Hartree-Fock and configuration interaction equations of two-electron systems. They investigate the accuracy of the method for the ground states and some of the excited states of H, He and H-. They illustrate the striking simplicity of the Hamiltonian matrix elements arising from the Lagrange functions properties when using the Gauss quadrature integration formula and test its accuracy as a function of the number of points defining the mesh. They also test the quality of the Lagrange function basis set by checking sum rules and by calculating the second-order energy of helium.
BibTeX:
@article{Godefroid1989,
  author = {Godefroid, M. and Lievin, J. and Heenen, P.-H.},
  title = {Laguerre meshes in atomic structure calculations},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1989},
  volume = {22},
  article number = {006},
  pages = {3119-3136},
  doi = {10.1088/0953-4075/22/20/006}
}
BibTeX:
@article{Kabbadj1989,
  author = {Kabbadj, Y. and Lievin, J.},
  title = {Ab initio study of the electronic structure of the PO2radical},
  journal = {Physica Scripta},
  year = {1989},
  volume = {40},
  pages = {259-269},
  doi = {10.1088/0031-8949/40/3/002}
}
Abstract: Theory is developed for the calculation of dipole transition line strengths and frequencies for rotational and ro-vibrational transitions from wavefunc-tions expressed in the generalized body-fixed co-ordinates proposed by Sutcliffe and Tennyson (1986, Molec. Phys., 58, 1053). Computations using this theory produce calculated frequencies for the fundamental ro-vibrational transitions of H2D+and D2H+in very good agreement with experiment. These first principles calculations use the highly accurate ab initio electronic potential energy and dipole surface of Meyer, Botschwina and Burton, which has previously been shown by the authors to give ro-vibrational transition frequencies, rotational constants and vibrational fundamentals of spectroscopic accuracy. Three line reassignments are proposed on frequency considerations. Several transitions are proposed as candidates for observation on the grounds of computed relative intensities. Calculated pure rotational transitions in ground state for H2D+and D2H+ are in excellent agreement with limited data available, and the full rotational spectra of these molecules are predicted. © 1989 Taylor & Francis Ltd.
BibTeX:
@article{Miller1989,
  author = {Miller, S. and Tennyson, J. and Sutcliffe, B.T.},
  title = {First principles calculation of rotational and ro-vibrational line strengths spectra for H2D+and D2H+},
  journal = {Molecular Physics},
  year = {1989},
  volume = {66},
  pages = {429-456},
  doi = {10.1080/00268978900100211}
}
Abstract: Calculations are presented of energy level values, radiative transition probabilities and autoionisation rates for terms belonging to the 1s 23l3l' configurations for several ions in the Be I isoelectronic sequence (C2+, N3+, O4+, Ne6+ and Xe50+). The results of a CI calculation including the configurations of the complex (and the 3d4f configuration) are compared with experimental results obtained in collisions of highly stripped ions with He, H2 and Ar and with the results of theoretical calculations.
BibTeX:
@article{Vaeck1989,
  author = {Vaeck, N. and Hansen, J.E.},
  title = {Calculations for 1s23l3l' states in C2+, N 3+, O4+, Ne6+ and Xe50+},
  journal = {Journal of Physics B: Atomic, Molecular and Optical Physics},
  year = {1989},
  volume = {22},
  article number = {007},
  pages = {3137-3153},
  doi = {10.1088/0953-4075/22/20/007}
}
BibTeX:
@article{Botschwina1988,
  author = {Botschwina, P. and Handy, N.C. and Halonen, L. and Gaw, J.F. and Ha, T.K. and Lewerenz, M. and Quack, M. and Sheppard, N. and Duncan, J.L. and Brodersen, S. and Baggott, J.E. and Law, D.W. and Lehmann, K.K. and Hutchinson, J.S. and Winnewisser, M. and Holme, T.A. and Carney, G.D. and Duxbury, G. and Tennyson, J. and Child, M.S. and Chambers, A.V. and Sutcliffe, B.T. and Jensen, P. and Marquardt, R. and Newnham, D.A. and Henry, B.R. and Mills, I.M. and Coy, S.L. and Caldow, G.L. and Smith, A.M. and Walsh, R. and Ashfold, M.N.R. and McKean, D.C. and Watts, R.O. and Carrasquillo, E. and Utz, A.L. and Crim, F.F. and Temps, F. and Santamaría, J. and Getino-Gonzalez, C. and Ezra, G.S. and Simons, J.P. and García-Ayllón, A. and Levine, R.D.},
  title = {General discussion},
  journal = {Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics},
  year = {1988},
  volume = {84},
  pages = {1555-1642},
  doi = {10.1039/F29888401555}
}
Abstract: The method of calculating interaction matrix elements between multi-configurational wave functions, given by Fano (1965) for orthogonal orbitals, is extended to allow the use of non-orthogonal orbitals. We allow up to two subshells in each configuration function which contain spectator (non-interacting) electrons described by orbitals which are not orthogonal to orbitals in the other configuration function of the matrix element. A discussion of the effects of less restrictive conditions is presented. © 1988.
BibTeX:
@article{Hibbert1988,
  author = {Hibbert, A. and Froese Fischer, C. and Godefroid, M.R.},
  title = {Non-orthogonal orbitals in MCHF or configuration interaction wave functions},
  journal = {Computer Physics Communications},
  year = {1988},
  volume = {51},
  pages = {285-293},
  doi = {10.1016/0010-4655(88)90141-5}
}
Abstract: The results of some highly accurate non-empirical ro-vibrational calculations on H2D+ are reported including some for J = 30 which are the first calculations to describe such a highly rotationally excited state. These results are obtained using an improved version of our algorithm. The method used is a variational one and is well adapted to execution on supercomputers. The computational characteristics of the performance the method on the CRAY 1s and the CRAY XMP 48 are given. © 1988.
BibTeX:
@article{Sutcliffe1988,
  author = {Sutcliffe, B.T. and Miller, S. and Tennyson, J.},
  title = {An effective computational approach to the calculation of the vibration-rotation spectra of triatomic molecules},
  journal = {Computer Physics Communications},
  year = {1988},
  volume = {51},
  pages = {73-82},
  doi = {10.1016/0010-4655(88)90063-X}
}
Abstract: Results are presented for nuclear motion calculations on D3+, H2D+ and the van der Waals complex ArCO in rotationally excited states. These calculations are performed using a two-step variational procedure which allows large ro-vibrational interactions (Coriolis couplings) to be treated accurately. The difficulty of assigning states in systems such as H2D+ where the Coriolis interactions are large is illustrated and the limitations of effective Hamiltonians derived from perturbation theory discussed.
BibTeX:
@article{Tennyson1988,
  author = {Tennyson, J. and Miller, S. and Sutcliffe, B.T.},
  title = {Beyond ro-vibrational separation},
  journal = {Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics},
  year = {1988},
  volume = {84},
  pages = {1295-1303},
  doi = {10.1039/F29888401295}
}
BibTeX:
@article{Urdaneta1988,
  author = {Urdaneta, C. and Largo-Cabrerizo, A. and Lievin, J. and Lie, G.C. and Clementi, E.},
  title = {Gaussian functions in hylleraas-Cl calculations. I. Ground state energies for H2, HeH+, and H3 +},
  journal = {The Journal of Chemical Physics},
  year = {1988},
  volume = {88},
  pages = {2091-2093}
}
Abstract: Multiconfiguration Hartree-Fock (MCHF) calculations are presented for singlet terms in neutral strontium (Sr i) belonging to (perturbed) sp, sd, and sf Rydberg series. We discuss briefly some particularly difficult MCHF calculations and the steps taken to overcome the difficulties. The ab initio wave functions are used to calculate radiative lifetimes as well as individual transition rates for electric dipole and quadrupole radiation. The calculated lifetimes are compared to recent experimental results. The observed trends are well reproduced by the calculations. We compare our wave functions with wave functions obtained from multichannel quantum-defect theory (MQDT) in either of two different ways. One is based on semiempirical fitting to the observed energy levels and the other on a recent ab initio R-matrix calculation of MQDT parameters. We find good agreement with the wave functions obtained in the latter calculation, confirming earlier conjectures about the degree of reliability of semiempirical MQDT fits to perturbed Rydberg series [C. Froese Fischer and J. E. Hansen, Phys. Rev. A 24, 631 (1981)]. © 1988 The American Physical Society.
BibTeX:
@article{Vaeck1988,
  author = {Vaeck, N. and Godefroid, M. and Hansen, J.E.},
  title = {Multiconfiguration Hartree-Fock calculations for singlet terms in neutral strontium},
  journal = {Physical Review A},
  year = {1988},
  volume = {38},
  pages = {2830-2845},
  doi = {10.1103/PhysRevA.38.2830}
}
Abstract: General mathematical expressions are derived for the weighting coefficients of the configuration state functions defining the singly excited function satisfying Brillouin's theorem for complex atomic configurations. The relations are illustrated for different cases and tested numerically by the cancellation of the Brillouin matrix elements using the Hartree-Fock solution for the reference function.
BibTeX:
@article{Godefroid1987,
  author = {Godefroid, M. and Lievin, J. and Metz, J.Y.},
  title = {Brillouin's theorem for complex atomic configurations},
  journal = {Journal of Physics B: Atomic and Molecular Physics},
  year = {1987},
  volume = {20},
  article number = {004},
  pages = {3283-3296},
  doi = {10.1088/0022-3700/20/14/004}
}
Abstract: The Racah fractional parentage coefficients (1943) used in atomic structure calculations contribute to a part of an ordinary unitary matrix transformation. In the present paper the authors describe three different approaches for completing this matrix using (i) projection operator techniques, (ii) the factorisation lemma of Racah and (iii) the spin-free formalism already used in theoretical studies of nuclear structures. The authors hope to give a deeper insight into the fractional parentage expansion and to its inverse transformation. © 1987, IOP Publishing Ltd.
BibTeX:
@article{Godefroid1987a,
  author = {Godefroid, M. and Lievin, J. and Metz, J.Y.},
  title = {Inversion of the fractional parentage matrix},
  journal = {Journal of Physics A: Mathematical and General},
  year = {1987},
  volume = {20},
  pages = {1645-1653},
  doi = {10.1088/0305-4470/20/7/011}
}
Abstract: Intracavity laser Stark experiments were performed on the v2 fundamental band of nitric acid, HNO3, using a CO laser. Despite the high density of observed resonances in the spectra, it was possible to recognize and fit several transitions. Calculations were made using a theoretical approach describing the Stark effect in asymmetric-topped molecules in terms of tensorial elements. The main result of the analysis was the first reported determination of the a and b components of the electric-dipole moment in the v2 = 1 vibrational level. © 1987, Optical Society of America.
BibTeX:
@article{Kleiner1987,
  author = {Kleiner, I. and Godefroid, M. and Herman, M. and Mc Kellar, A.R.W.},
  title = {Infrared laser Stark spectrum of HNO3 at 6 μm},
  journal = {Journal of the Optical Society of America B: Optical Physics},
  year = {1987},
  volume = {4},
  pages = {1159-1164},
  doi = {10.1364/JOSAB.4.001159}
}
Abstract: Variational rovibrational calculations performed on the molecules H2O and CH+2 are discussed with a view to pin-pointing the best solution strategy for each system. While all the methods discussed appeared to be reliable for the low-lying levels of water, CH+2 has proved a more testing system. A recently proposed method for calculating highly rotationally excited states is applied to the J = 10 levels of CH+2. Comparison of these calculations with those of Carter and Handy suggests that at this level of rotational excitation it will be necessary to consider full rovibronic coupling effects in the characterisation of any spectra of this floppy system.
BibTeX:
@article{Sutcliffe1987,
  author = {Sutcliffe, B.T. and Tennyson, J.},
  title = {Variational methods for the calculation of rovibrational energy levels of small molecules},
  journal = {Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics},
  year = {1987},
  volume = {83},
  pages = {1663-1674},
  doi = {10.1039/F29878301663}
}
Abstract: The advent of supercomputers has led to great advances in electronic structure calculations and to the ab initio calculation of molecular spectra. Recent theoretical developments have allowed us to develop a two-step variational algorithm for the calculation of rotationally highly excited states of floppy molecules. This algorithm allows highly accurate nuclear motion calculations to be performed on low-lying ro-vibrational states and greatly extends the range of states that can practicably be considered. The algorithm has been adapted to run efficiently on the Cray supercomputers. Analysis of the timings suggest that construction of the secular matrix is highly vectorised and that the special structure of secular matrix can be used to give rapid diagonalisation. The limiting factor on these calculations is the available fast storage, but analysis suggests that this bottleneck could be removed by use of a Solid State Device (SSD). Sample results are given for calculations involving a range of rotational excitation. An adaptation of the algorithm to a loop of parallel processors is also suggested. © 1987 Springer-Verlag.
BibTeX:
@article{Sutcliffe1987a,
  author = {Sutcliffe, B.T. and Tennyson, J. and Miller, S.},
  title = {The use of supercomputers for the variational calculation of ro-vibrationally excited states of floppy molecules},
  journal = {Theoretica Chimica Acta},
  year = {1987},
  volume = {72},
  pages = {265-276},
  doi = {10.1007/BF00529031}
}
Abstract: The multi-configuration Hartree-Fock method, extended to include relativistic effects in the Breit-Pauli approximation (MCHF+BP), has been applied to the study of some forbidden transitions between levels of the 3s 23p3 configuration in the phosphorus sequence. Term energy separations, fine-structure splittings, and E2 and M1 transition rates are reported for S II of interest in astrophysics and for several atomic systems with nuclear charge, Z, in the range 28<or=Z<or=42, where lines have been observed in laboratory plasmas. The results are compared with values derived from observation and with other theories.
BibTeX:
@article{Fischer1986,
  author = {Fischer, C.F. and Godefroid, M.},
  title = {Multi-configuration Hartree-Fock plus Breit-Pauli results for some forbidden transitions},
  journal = {Journal of Physics B: Atomic and Molecular Physics},
  year = {1986},
  volume = {19},
  article number = {004},
  pages = {137-148},
  doi = {10.1088/0022-3700/19/2/004}
}
Abstract: The five lowest states of both2∑+ and2π symmetries were calculated with a large STO basis set (24σ, 13π, 55δ, including Rydberg orbitals on Be and on H), over a wide range of interatomic distances. A two-step Cl procedure (singles, doubles and triples over the valence shell) involving each 2899 and 4122 CSF’s for2∑+ and2π states respectively was used throughout the work. The results include term energies (also of dissociation products), dissociation energies, spectroscopic constants and dipole moments. The agreement between calculated results and available experimental data indicates a precision of  400cm-1 in the energies   0.005Å in the equilibrium internuclear distances and   15 cm-1 in the vibration frequencies. The states are analysed as a function of intemuclear distance by means of their natural orbitals, and semi-quantitive information is obtained concerning the validity of the Bom-Oppenheimer approximation for certain states at certain distances. Finally, experimental interpretations of observed anomalies are rationalized. © 1986 IOP Publishing Ltd.
BibTeX:
@article{Henriet1986,
  author = {Henriet, C. and Verhaegen, G.},
  title = {Accurate calculation of the excited states of the molecule beh},
  journal = {Physica Scripta},
  year = {1986},
  volume = {33},
  pages = {299-309},
  doi = {10.1088/0031-8949/33/4/004}
}
Abstract: A generalization of the well known atom-diatom scattering hamiltonian to a coordinate system of two lengths and an angle is derived, another special case of which is a previously known bond angle-bond length hamiltonian. Different axis embeddings are also considered. The formalism is applied to the ro-vibrational levels of D2H+, CH2+ and HDHe (A1A’) and the advantage of a judicious choice of coordinates demonstrated. The vibrational band origins for HDHe*, the first predictions for this system for which previous calculations had failed, are obtained using a new geometrically defined coordinate system. It is suggested that these coordinates might be used to represent isotopically substituted van der Waals complexes. © 1986 Taylor & Francis Group, LLC.
BibTeX:
@article{Sutcliffe1986,
  author = {Sutcliffe, B.T. and Tennyson, J.},
  title = {A generalized approach to the calculation of ro-vibrational spectra of triatomic molecules},
  journal = {Molecular Physics},
  year = {1986},
  volume = {58},
  pages = {1053-1066},
  doi = {10.1080/00268978600101801}
}
Abstract: The state‐of‐the‐art in non‐empirical calculations of potential energy surfaces for small molecules is discussed, as is the present position with respect to the analytic fitting of such surfaces. The results of some nonempirical vibration‐rotation calculations performed on such analytic surfaces are presented and compared with experimental results. An attempt is made to assess the extent to which present methods of electronic structure calculation and present analytic fitting methods are adequate to produce surfaces for the interpretation of high‐resolution spectral data. Copyright © 1986 John Wiley & Sons, Inc.
BibTeX:
@article{Sutcliffe1986a,
  author = {Sutcliffe, B.T. and Tennyson, J.},
  title = {The construction and fitting of molecular potential energy surfaces and their use in vibration‐rotation calculations},
  journal = {International Journal of Quantum Chemistry},
  year = {1986},
  volume = {30},
  pages = {507-520},
  doi = {10.1002/qua.560300744}
}
Abstract: A partitioning of the generalized triatomic hamiltonian of the preceding paper is developed which allows the calculation of highly-excited rotational states, without approximation, in a two-step variational procedure. Iterative diagonalization techniques are found to be particularly useful for the second variational step. The rotationally-excited states of H2D+ are studied with J≤20, well into the region where the ground and excited state manifolds overlap. Comparison of results for two different ab initio potentials and convergence considerations suggest that pure rotational transition frequencies obtained from our results should be accurate to about 1 cm-1 for J 15. © 1986 Taylor & Francis Group, LLC.
BibTeX:
@article{Tennyson1986a,
  author = {Tennyson, J. and Sutcliffe, B.T.},
  title = {Highly rotationally excited states of floppy molecules: H2D+ with j≤20},
  journal = {Molecular Physics},
  year = {1986},
  volume = {58},
  pages = {1067-1085},
  doi = {10.1080/00268978600101811}
}
Abstract: H3 + and its isotopomers are seen as a benchmark for the comparison of theory and experiment. The stages of an ab initio calculation (electronic structure, potential fitting and nuclear motion) are discussed and the sources of error highlighted by consideration of recent results. Fitting of the electronic structure data is seen to be an area needing more development. New results are presented for the low-lying rovibrational states of D3 +. While rovibrational properties can be calculated in the low-energy region to within ca. 0.1% accuracy, the high-energy region is still largely unexplored. New developments in the calculation of excited rotational states (J ≤ 20) are outlined and the possibility of quantum-mechanical calculations of vibrational levels in the near-dissociation region is discussed in the light of illustrative calculations.
BibTeX:
@article{Tennyson1986,
  author = {Tennyson, J. and Sutcliffe, B.T.},
  title = {The infrared spectrum of H3 + and its isotopomers. A challenge to theory and experiment},
  journal = {Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics},
  year = {1986},
  volume = {82},
  pages = {1151-1162},
  doi = {10.1039/F29868201151}
}
Abstract: Accurate multiconfiguration Hartree-Fock calculations were performed to investigate the J-dependence of the lifetimes of 3s4p3P°J (J = 2, 1, 0) in S V and Cl VI. The relativistic corrections have been included through the Breit-Pauli approximation. The variation with J, observed in S V but not in Cl VI [4], is explained by the selective opening of decay channels resulting from the triplet-singlet mixing and by the J-dependence found in the El spin-allowed transition decay rates where the coulomb and relativistic configuration interaction between 3s4p and 3p3d play a crucial role. The effects of the relativistic shift corrections on the wavefunction compositions and transition probabilities are discussed. New gf-values are reported for the singlet-singlet electric dipole transistions from 3s4p1P°1, taking into account the1P-character loss due to the inter-symmetry mixing. © 1985 IOP Publishing Ltd.
BibTeX:
@article{Godefroid1985a,
  author = {Godefroid, M. and Froese Fischer, C.},
  title = {Relativistic and correlation effects on the lifetimes of 3s4p3p°j levels in mg-like sulphur and chlorine},
  journal = {Physica Scripta},
  year = {1985},
  volume = {31},
  pages = {237-245},
  doi = {10.1088/0031-8949/31/4/004}
}
Abstract: Quantitative comparisons between observed and theoretical wavelengths and intensity ratios are made to confirm the identification of some emission lines observed in the spectra of Na- and Mg-like ions as electric quadrupole (E2) transitions. The transition rates of these lines connecting D symmetry levels and the ground level are calculated using the multiconfiguration Hartree-Fock (MCHF) wavefunctions. © 1985 IOP Publishing Ltd.
BibTeX:
@article{Godefroid1985,
  author = {Godefroid, M. and Magnusson, C.E. and Zetterberg, P.O. and Joelsson, I.},
  title = {Forbidden transitions in na− and mg-like spectra},
  journal = {Physica Scripta},
  year = {1985},
  volume = {32},
  pages = {125-128},
  doi = {10.1088/0031-8949/32/2/006}
}
Abstract: A simplified method for molecular correlation energy calculations developed in I is applied to the determination of the potential curves of some diatomic chlorinated molecules HCl(1Σ+), HCl+(2II), ClO(2II) and NCl(X3Σ-, a1Δ, b1Σ+). Dissociation energies, vibrational frequencies and equilibrium internuclear distances are derived from these curves. The ionisation potential (Ip) of HCl, the proton affinity (PA) of Cl, and the term energies of the excited states of the NCl radical are also calculated. It is shown that the results are very sensitive to correlation effects and that the correlated results converge to the corresponding experimental values within 10% for PA, De, Te and ωe, 2% for Re and 0.3% for Ip. This agreement allows us to predict the following lower limits for the dissociation energies of the NCl radical: 2.14, 3.28 and 2.47 eV respectively for the X3Σ-, a1Δ and b1Σ+ states. Results on HF and HF+ are also discussed and compared with those obtained for HCl and HCl+. © 1985 Springer-Verlag.
BibTeX:
@article{Lievin1985,
  author = {Lievin, J. and Metz, J.-Y.},
  title = {Extension of a simplified method for molecular correlation energy calculations to molecules containing third row atoms II. Application to HCl, HCl+, ClO and NCl molecules},
  journal = {Theoretica Chimica Acta},
  year = {1985},
  volume = {67},
  pages = {391-407},
  doi = {10.1007/BF00530089}
}
Abstract: This report is concerned with the calculation of molecular wavefunctions and consist of two parts: the first provides an over-view of the development of various forms of self-consistent field (SCP) theory, from the early work of Hartee and collaborators (on atoms) up to the present day; while tehsecond turns to the systematic improvement of approximations at the Hartee-Fock (HF) level by the admission of configuration interaction (CI). The emphasis of the report is on the development of methodology, always in a form well adapted to computer implementation, but considerations of a purely computational nature are excluded. The aim is rather to provide a coherent review of one sector of a large and rapidly expanding area of computational physics - the calculation and use of high-precision electronic wavefunctions for molecules - and to provide a general introduction to other reports in this series. Part I deals first with the traditional approach to the problem of optimizing the orbitals in a one-determinant wavefunctions, as applied in the closed-shell, retricted and unrestricted forms of the HF approximation. This is followed by the introduction of second-quantization techniques and a more detailed discussion of solution methods. Part II is concerned with the general problem of constructing high-precision wavefunctions as truncated complete-set expansions containing thousands, sometimes millions, of terms. Recent progress is discussed, with emphasis on the exploitation of permutation and unitary group symmetries, the efficient evaluation of matrix elements, and the development of algorithms for solving very high order matrix eigenvalue equations. © 1984.
BibTeX:
@article{McWeeny1985,
  author = {McWeeny, R. and Sutcliffe, B.T.},
  title = {Fundamentals of Self-Consistent-Field (SCF), Hartree-Fock (HF), Multi-Configuration (MC)SCF and Configuration Interaction (CI) schemes},
  journal = {Computer Physics Reports},
  year = {1985},
  volume = {2},
  pages = {219-278},
  doi = {10.1016/0167-7977(85)90009-7}
}
Abstract: An extension of a simplified method for molecular correlation energy calculations to molecules containing third row atoms is presented. In addition to the use of pseudo-potentials in the calculations, the consequences of this extension on the different components of the energy partition which is the basic idea of the method, is analysed. Particular emphasis is placed on the specific role played by the 3 d orbitals in each of the energy components. First, at the zeroth order, the energy is found to be very sensitive to the optimization of the 3 d polarization functions. Secondly, the internal correlation energy, calculated by CI, requires the optimization of distinct 3 d correlation orbitals to describe adequately the strong near-degeneracy effects that occur within the valence space. Finally it is shown that the 3 d orbitals contribute partially to the non-internal correlation energy and that, the "atoms-in-molecule" structures corresponding typically to all-external contributions are negligible. The concept of error energy is introduced in place of the non-internal correlation energy: it includes the relativistic contributions within the semi-empirical tables. Such tables are presented for second row atoms and for the chlorine atom. From these tables, predicted values for some atomic term energies, experimentally undetermined, are derived. The methodological tests are limited here to the chlorine atom which is chosen for further applications in the next paper of this series. The conclusions concerning the applicability of the method to third row atoms are however quite general. © 1985 Springer-Verlag.
BibTeX:
@article{Metz1985,
  author = {Metz, J.-Y. and Lievin, J.},
  title = {Extension of a simplified method for molecular correlation energy calculations to molecules containing third row atoms. I. Methodological developments},
  journal = {Theoretica Chimica Acta},
  year = {1985},
  volume = {67},
  pages = {369-390},
  doi = {10.1007/BF00530088}
}
Abstract: Variationally exact rovibrational calculations are performed for the H3 +, H2D+ and D2H+ molecules using two recent fits to the ab initio potential energy data of Burton et al. (1985, Molec. Phys., 55, 527). For the best surface, vibrational fundamentals are vA1 = 3175 cm-1 and νE = 2518 (2521) cm-1 for H3 + ; νl = 2989 (2992) cm-1, ν2= 2203 cm-1, and ν3 = 2332cm-1 for H2D+ , and νt = 2733 (2737), ν2 = 1965, ν3 = 2027 for D2H+ (where experimental results are given in parenthesis). Rotational constants, which agree well with the experimental constants, where available, are calculated for H3 + and D2H+ . Results are presented for the (0, 1, 0) and (0, 0, 1) states of D2H+ which are yet to be characterized experimentally. © 1985 Taylor & Francis Group, LLC.
BibTeX:
@article{Tennyson1985,
  author = {Tennyson, J. and Sutcliffe, B.T.},
  title = {A calculation of the rovibrational spectra of the H+ 3, H2D+ and D2H+ molecules},
  journal = {Molecular Physics},
  year = {1985},
  volume = {56},
  pages = {1175-1183},
  doi = {10.1080/00268978500102981}
}
Abstract: Ab initio data for the rotational levels of the (0, 0, 0), (0, 1, 0) and (0, 0, 1) states of H2D+ are fitted and assignments suggested for the spectrum of Shy, Farley and Wing (1981, Phys. Rev., A, 24, 1146). © 1985 Taylor and Francis Group, LLC.
BibTeX:
@article{Tennyson1985a,
  author = {Tennyson, J. and Sutcliffe, B.T.},
  title = {Calculated ro-vibrational spectrum of H2D+},
  journal = {Molecular Physics},
  year = {1985},
  volume = {54},
  pages = {141-144},
  doi = {10.1080/00268978500100111}
}
Abstract: The multiconfiguration Hartree-Fock method extended to include relativistic effects in the Breit-Pauli approximation (MCHF-BP) is tested in the study of the ground configuration of nitrogen-like ions. Fine-structure splittings, E2 and M1 transition rates calculated with the classical (nonrelativistic) form of the magnetic transition operator are presented and compared with other theoretical and experimental results up to Zn XXIV. The astrophysical problem of the high-density limit of the intensity ratio I(2D5/2 to 4S3/2)/I(2D3/2 to 4S 3/2) is discussed on the basis of these new theoretical data.
BibTeX:
@article{Godefroid1984,
  author = {Godefroid, M. and Fischer, C.F.},
  title = {MCHF-BP fine-structure splittings and transition rates for the ground configuration in the nitrogen sequence},
  journal = {Journal of Physics B: Atomic and Molecular Physics},
  year = {1984},
  volume = {17},
  article number = {008},
  pages = {681-692},
  doi = {10.1088/0022-3700/17/5/008}
}
Abstract: Accurate ab initio LCAO-MO-SCF-CI calculations were performed at a series of internuclear distances in order to obtain the potential energy curves for the five lowest states of 2Σ+ symmetry and the four lowest of 2Π symmetry. A large STO basis set including Rydberg orbitals (RO) was used. The CI calculations were carried out in two steps, the first without including the RO's, the second including them together with the leading NO's of the first CI calculation. The results are in excellent agreement with available experimental values. Calculations were run with ALCHBXL (ref.1), an adapted version of ALCHEMY (ref.2) to CDC CYBER 170 computers. © 1984.
BibTeX:
@article{Henriet1984,
  author = {Henriet, C. and Verhaegen, G.},
  title = {Valence and Rydberg states of the BeH molecule},
  journal = {Journal of Molecular Structure: THEOCHEM},
  year = {1984},
  volume = {107},
  pages = {63-73},
  doi = {10.1016/0166-1280(84)80038-X}
}
Abstract: A simplified method for molecular correlation energy calculations has been recently proposed (ref. 1-2) on the basis of a partition into internal and non-internal contributions. The field of application of the method is discussed, some typical results are commented and recent developments are presented. The formalism of the "atoms-in-molecule" approach adopted for the non-internal correlation energy calculations is analyzed in order to optimize its programming. The extension of the method to molecules containing atoms of the third row is considered and particular emphasis is layed on the choice of semi-empirical atomic data. Finally, preliminar results obtained for the Chlorine atom are presented. © 1984.
BibTeX:
@article{Lievin1984,
  author = {Lievin, J. and Metz, J.Y.},
  title = {Semi-empirical calculation of the molecular correlation energy},
  journal = {Journal of Molecular Structure: THEOCHEM},
  year = {1984},
  volume = {107},
  pages = {23-38},
  doi = {10.1016/0166-1280(84)80034-2}
}
Abstract: A semi-empirical method for electronic correlation energy calculations, recently proposed by Liévin and al. (refs.1,3), is discussed in regard to its domain of applicability. Although the economical version of this method was primarily limited to the calculation of reaction energies, it is proposed here to extend the use of this version to the study of potential surfaces associated with the fundamental state of a supermolecule. A few points of the potential surface of 2 CN are examined as an example. © 1984.
BibTeX:
@article{Moreau1984,
  author = {Moreau, B. and Sana, M. and Leroy, G. and Lievin, J.},
  title = {Contribution to the semi-empirical calculation of electronic correlation hypersurfaces},
  journal = {Journal of Molecular Structure: THEOCHEM},
  year = {1984},
  volume = {107},
  pages = {111-115},
  doi = {10.1016/0166-1280(84)80045-7}
}
Abstract: Variationally exact rovibrational levels for the H3+ and H2D+ molecules are calculated using a recently published accurate potential. Vibrational fundamentals are vA1 = 3191 cm-1 and vE = 2494 (2521-6) cm-1 for H3+ and v1 = 3000 cm-1, v2 = 2184 cm-1 and v3 = 2310 cm-1 for H2D+. For H3+ calculated ground state rotational constants are B0 = 43-51 (43-57) cm-1, C„ = 20-59 (20-71) cm-1, Dj0 = 0-04 (0-05) cm-1, DJK0= -0-07 (-0-10) cm-1 and Dk = 0-04 (0-04) cm-1 (where experimental results are given in parenthesis). An attempt is made to stabilize many vibrational states. We thus reassess the results of Carney and Porter. The implications for astrophysics, the interpretation of the infrared spectrum of H3+ near its dissociation limit and the unassigned spectrum of H2D+ are discussed. © 1984 Taylor & Francis Group, LLc.
BibTeX:
@article{Tenyson1984,
  author = {Tenyson, J. and Sutcliffe, B.T.},
  title = {On the rovibrational levels of the H3+ and H2D+ molecules},
  journal = {Molecular Physics},
  year = {1984},
  volume = {51},
  pages = {887-906},
  doi = {10.1080/00268978400100591}
}
Abstract: A simplified method of correlation energy calculation has been recently proposed (ref. 1-2). This method, which was shown to give good reaction heats where H.F. calculation fails (dissociations) is tested here in the calculation of reaction heats for which the H.F. approximation gives good results. © 1983.
BibTeX:
@article{Breuletx1983,
  author = {Breuletx, J. and Lievin, J.},
  title = {Study of correlation effects in the calculation of heats of reactions.},
  journal = {Journal of Molecular Structure: THEOCHEM},
  year = {1983},
  volume = {93},
  pages = {341-345},
  doi = {10.1016/0166-1280(83)80123-7}
}
Abstract: We combine earlier treatments for the embedding of body-fixed coordinates in linear molecules with the close-coupling formalism developed for atom- diatom scattering and derive a hamiltonian which is most convenient for describing the nuclear motions in van der Waals complexes and other non-rigid Systems comprising two polyatomic fragments, A and B. This hamiltonian can stili be partitioned in the form Ha + Hb + HINT, just as the space-fixed hamiltonian. The body-fixed form, however, has several advantages. We discuss solution strategies for the rovibrational problem in non-rigid dimers, based on this partitioning of the hamiltonian. Finally, in view of the size of the generai polyatomic-polyatomic case, we suggest problems which should be currently practicable. © 1983 Taylor & Francis Group, LLC.
BibTeX:
@article{Brocks1983,
  author = {Brocks, G. and Van Der Avoird, A. and Sutcliffe, B.T. and Tennyson, J.},
  title = {Quantum dynamics of non-rigid systems comprising two polyatomic fragments},
  journal = {Molecular Physics},
  year = {1983},
  volume = {50},
  pages = {1025-1043},
  doi = {10.1080/00268978300102831}
}
BibTeX:
@article{Carter1983,
  author = {Carter, S. and Handy, N.C. and Sutcliffe, B.T.},
  title = {Preliminary communication: A variational method for the calculation of rovibrational levels of any triatomic molecule},
  journal = {Molecular Physics},
  year = {1983},
  volume = {49},
  pages = {745-748},
  doi = {10.1080/00268978300101521}
}
Abstract: A simplified method for the calculation of molecular correlation energies, developed previously, is applied to the study of the potential energy hypersurface related to the reaction O2+H→HO2→OH+O. The main parameters that characterize the topology of the surface have been determined: the equilibrium geometries and vibrational frequencies of HO2 and of its dissociation products, the dissociation energies, the energy gap between the dissociation limits, the geometry of an activated complex, and the corresponding potential barrier height. The particular importance of including the correlation energy is discussed for each of the calculated parameters. In spite of the minimal computational effort required, the results are in good agreement with the experimental data on the one hand, and with the results proceeding from elaborate variational calculations on the other hand. Moreover the controverted existence of a potential barrier (0.19 eV) along the O2+H→ HO2 recombination path is discussed. © 1983 Springer-Verlag.
BibTeX:
@article{Metz1983,
  author = {Metz, J.-Y. and Lievin, J.},
  title = {Application of an economical method for the calculation of molecular correlation energies to the study of a potential energy surface: The HO2 radical dissociation process},
  journal = {Theoretica Chimica Acta},
  year = {1983},
  volume = {62},
  pages = {195-207},
  doi = {10.1007/BF00548834}
}
Abstract: In a recent paper Carter and Handy recommended the use generally of a particular form of the vibration-rotation hamiltonian for a triatomic molecule. The grounds on which this recommendation is made are examined and shown to be inadequate. A detailed examination of the properties of the proposed hamiltonian is undertaken and some suggestions about its likely domain are made. © 1983 Taylor & Francis Group, LLC.
BibTeX:
@article{Sutcliffe1983,
  author = {Sutcliffe, B.T.},
  title = {A comment on a recent proposal for the calculation of vibrational energies in the general triatomic molecule},
  journal = {Molecular Physics},
  year = {1983},
  volume = {48},
  pages = {561-566},
  doi = {10.1080/00268978300100391}
}
Abstract: Ro-vibrational calculations are performed on the CH2+ radical using a method recently developed for atom-diatom systems. The vibrational fundamentals obtained are 2998.8, 718.3, and 3270.7 cm-1, in good agreement with recent results. Band origins for several higher vibrational levels are also obtained. Calculations with J = 1 show that the Coriolis interaction play a significant role and two alternative embeddings are discussed. Use of correlation parameters confirms that CH2+ belongs to no idealized class of molecules in keeping with its "floppy" nature. © 1983.
BibTeX:
@article{Tennyson1983a,
  author = {Tennyson, J. and Sutcliffe, B.T.},
  title = {Variationally exact ro-vibrational levels of the floppy CH2+ molecule},
  journal = {Journal of Molecular Spectroscopy},
  year = {1983},
  volume = {101},
  pages = {71-82},
  doi = {10.1016/0022-2852(83)90007-3}
}
Abstract: A variationally exact method of obtaining the rovibrational levels of triatomic potentials is presented. This LC-RAMP method derives from the close-coupling approach in body-fixed coordinates, but uses optimized Morse oscillator functions to give radial basis sets for both the diatomic and complex stretching coordinates. The method is suited to the nuclear dynamics of nonrigid molecules and atom-diatom van der Waals complexes. A recent full interaction surface for HeHF is fitted and used for dynamical calculations. The binding energy of the complex increases slowly with HF vibrational excitation. Correlation between the HF and complex vibrational modes is found to be negligible. © 1983 American Institute of Physics.
BibTeX:
@article{Tennyson1983,
  author = {Tennyson, J. and Sutcliffe, B.T.},
  title = {Variationally exact rovibrational spectra of nonrigid triatomics: The HeHF van der Waals molecule},
  journal = {The Journal of Chemical Physics},
  year = {1983},
  volume = {79},
  pages = {43-51}
}
Abstract: An ab initio study of the electronic structure of several 22-electrons molecules is presented. The equilibrium geometries of their ground state are calculated at the SCF level using the 6-31G basis set and are found to be in good agreement with the experimental geometries. The dissociation process of these molecules leading to the isoelectronic products CO or N2 on the one hand and BH3, CH2, NH and O on the other hand is studied. The least-energy dissociation paths of the ground states determined at the SCF level are compared on the basis of electron density interactions. The dissociation energies corresponding to the two lowest dissociation channels are calculated. In these calculations, the correlation energy is taken into account using a non-variational method developed previously. The calculated values of dissociation energies are in good agreement with the existing experimental values. The results permit to predict values for HNCO, BH3CO and CH2N2 and to confirm the instability of BH3N2. © 1982 Springer-Verlag.
BibTeX:
@article{Breulet1982,
  author = {Breulet, J. and Lievin, J.},
  title = {Comparative theoretical study of the dissociation process of the isoelectronic molecules BH3CO, CH2CO, HNCO, CO2 and BH3N2, CH2N2, HN3, N2O},
  journal = {Theoretica Chimica Acta},
  year = {1982},
  volume = {61},
  pages = {59-72},
  doi = {10.1007/BF00573865}
}
Abstract: Theoretical lifetime trends are reported for all bound singlet states in the n=3 complex of the Mg sequence for Z≤26. Calculations are based on MCHF wavefunctions and include only dipole allowed transitions in the LS scheme. For states that are entering the bound spectrum, the reported lifetime is an upper bound. At sufficiently high Z, all these states can decay only through Δn=0 transitions and several lifetime trends become similar. Implications for the cascade problem in beam-foil spectroscopy are discussed. © 1982.
BibTeX:
@article{Fischer1982,
  author = {Fischer, C.F. and Godefroid, M.},
  title = {Lifetime trends for the n=3 singlet states in the Mg sequence},
  journal = {Nuclear Instruments and Methods In Physics Research},
  year = {1982},
  volume = {202},
  pages = {307-322},
  doi = {10.1016/0167-5087(82)90411-2}
}
Abstract: Relations between magnetic radial integrals are derived and used in the discussion of symmetry properties of mutual spin-orbit matrix elements.
BibTeX:
@article{Godefroid1982,
  author = {Godefroid, M.},
  title = {Note on the mutual spin-orbit matrix elements},
  journal = {Journal of Physics B: Atomic and Molecular Physics},
  year = {1982},
  volume = {15},
  article number = {008},
  pages = {3583-3586},
  doi = {10.1088/0022-3700/15/20/008}
}
BibTeX:
@article{Herman1982,
  author = {Herman, M. and Lievin, J.},
  title = {Acetylene from intensity alternation in spectra to ortho and para molecules},
  journal = {Journal of Chemical Education},
  year = {1982},
  volume = {59},
  pages = {17-21}
}
BibTeX:
@article{Lievin1982,
  author = {Lievin, J.},
  title = {Plots of potential curves and vibritional levels},
  journal = {Journal of Chemical Education},
  year = {1982},
  volume = {59},
  pages = {777-778}
}
Abstract: A simplified method of determining the molecular correlation energy by two separate calculations, one for the internal and one for the non-internal correlation energies, is extended to multiconfigurational zeroth-order wavefunctions. This extension offers the possibility of deriving correlated potential energy curves or surfaces for processes involving configurational changes. The internal correlation energy is shown to be correctly determined by an MC/CI procedure combining the use of minimal and extended basis sets. An original semi-empirical “atoms-in-molecules” method based on the L.C.A.O. expansion of the molecular wavefunction is proposed for the non-internal correlation energy calculations. This method is shown to be able to overcome some of the shortcomings of a previous populations analysis approach. Test calculations concern potential curve parameters (De, Te, Re, We) of the ground and some excited states of the NH, C2, HCN and CN molecules. The results are found to be in good agreement with corresponding experimental and large CI results. © 1982, Springer-Verlag. All rights reserved.
BibTeX:
@article{Lievin1982a,
  author = {Lievin, J. and Breulet, J. and Clercq, P. and Metz, J.},
  title = {A simplified method for molecular correlation energy calculations by separation into internal and non-internal parts. Application to multiconfigurational zeroth-order wavefunctions},
  journal = {Theoretica chimica acta},
  year = {1982},
  volume = {61},
  pages = {513-537},
  doi = {10.1007/PL00020139}
}
Abstract: Separate optimized s and p bond functions (BFs) were added to the corresponding Dunning basis sets (11s,6p15s) → (5s,4p13s) for the four hydrides. Properties calculated with these basis sets are quasi-identical to those obtained with conventional polarization functions (dlp). The computer time ratios found are: t(BF)/t(dlp) = 1 2 for UHF calculations, and 2 3 for MC SCF calculations. © 1982.
BibTeX:
@article{Neisius1982,
  author = {Neisius, D. and Verhaegen, G.},
  title = {Bond functions for AB initio calculations. MCSCF results for CH, NH, OH and FH},
  journal = {Chemical Physics Letters},
  year = {1982},
  volume = {89},
  pages = {228-233},
  doi = {10.1016/0009-2614(82)80047-X}
}
Abstract: Dynamical calculations are performed on an ab initio potential energy surface for KCN. Approximate variational solutions of the vibrational Eckart hamiltonian are presented for several states. Fundamental vibrations are found to lie at 302-7 cm-1 and 119-7 cm-1. An effective rotational hamiltonian is solved for several vibrational states allowing vibrational assignments to be made to the observed rotational spectrum. © 1982 Taylor & Francis Group, LLC.
BibTeX:
@article{Tennyson1982a,
  author = {Tennyson, J. and Sutcliffe, B.T.},
  title = {Ab initio vibrational-rotational spectrum of potassiumcyanide: Kcn},
  journal = {Molecular Physics},
  year = {1982},
  volume = {46},
  pages = {109},
  doi = {10.1080/00268978200101101}
}
Abstract: A Hamiltonian for the vibration-rotation motions of atom-diatom systems is derived in body-fixed coordinates and a method for its solution as a close-coupled secular problem is formulated. The radial coordinate is expanded in Morse oscillator functions. Calculations on KCN and H2Ne are presented. For KCN the neglect of Coriolis interactions is found to have little effect. Extensions of the method to problems in more dimensions are suggested. © 1982 American Institute of Physics.
BibTeX:
@article{Tennyson1982,
  author = {Tennyson, J. and Sutcliffe, B.T.},
  title = {The ab initio calculation of the vibrational-rotational spectrum of triatomic systems in the close-coupling approach, with KCN and H2Ne as examples},
  journal = {The Journal of Chemical Physics},
  year = {1982},
  volume = {77},
  pages = {4061-4072}
}
Abstract: Nonempirical molecular structure calculations were performed to obtain an electronic potential energy surface for the CH2+ radical. The vibrational Eckart Hamiltonian was approximately solved on this surface using a variational method, with basis functions designed to allow for the singular behavior of the Eckart Hamiltonian as the radical becomes linear. © 1981.
BibTeX:
@article{Bartholomae1981,
  author = {Bartholomae, R. and Martin, D. and Sutcliffe, B.T.},
  title = {A nonempirical calculation of the lowest vibrational band origins for the CH2+ radical using a novel vibrational wavefunction},
  journal = {Journal of Molecular Spectroscopy},
  year = {1981},
  volume = {87},
  pages = {367-381},
  doi = {10.1016/0022-2852(81)90409-4}
}
Abstract: Theoretical lifetime trends are reported for all bound singlet states in the n equals 3 complex of the Mg sequence for Z less than equivalent to 26. Calculations are based on MCHF wavefunctions and include only dipole allowed transitions in the LS scheme. For states that are entering the bound spectrum, the reported lifetime is an upper bound. At sufficiently high Z, all these states can decay only through DELTA n equals 0 transitions and several lifetime trends become similar. Implications for the cascade problem in beam-foil spectroscopy are discussed.
BibTeX:
@article{FroeseFischer1981,
  author = {Froese Fischer, C. and Godefroid, M.},
  title = {LIFETIME TRENDS FOR THE n equals 3 SINGLET STATES IN THE Mg SEQUENCE.},
  journal = {Nuclear instruments and methods in physics research},
  year = {1981},
  volume = {202},
  pages = {307-322},
  doi = {10.1016/0167-5087(82)90411-2}
}
Abstract: A simple and economical method for molecular correlation energy calculations is developed. In this method, the internal part of the correlation energy is calculated by means of a CI in a minimal basis set and the non-internal part (semi-internal and all-external) is evaluated using an original "atoms-in-molecule" method. It is successfully applied to the determination of dissociation energies of some diatomic (H2, NH, C2, CN, N2, CO, NO, O2, F2) and polyatomic (H2O, N2O, CO2, N3H, CH2N2, CH2CO, C2N2) molecules. The results are compared to those obtained using very elaborate variational methods. © 1981 Springer-Verlag.
BibTeX:
@article{Lievin1981,
  author = {Lievin, J. and Breulet, J. and Verhaegen, G.},
  title = {A method for molecular correlation energy calculations. Application to the determination of dissociation energies of diatomic and polyatomic molecules},
  journal = {Theoretica Chimica Acta},
  year = {1981},
  volume = {60},
  pages = {339-353},
  doi = {10.1007/BF00549277}
}
Abstract: Parameters (exponent and position) have been optimized for bond functions and lone-pair functions to be added to basis sets 6-31G. Single average values are proposed for: C-H: N-H and O-H; C-C; C-N, C-O, N-N, N-O and O-O bonds; and all lone pairs on C, N and O. Test calculations favour this type of polarization function with respect to traditional d functions. © 1981.
BibTeX:
@article{Neisius1981,
  author = {Neisius, D. and Verhaegen, G.},
  title = {Bond functions for ab initio calculations on polyatomic molecules. Molecules containing C, N, O and H},
  journal = {Chemical Physics Letters},
  year = {1981},
  volume = {78},
  pages = {147-152},
  doi = {10.1016/0009-2614(81)85573-X}
}
Abstract: SCF-CI calculations were done on tetratomic oxygen complexes at various geometries. The results point to the existence of a metastable covalent molecule O4 completely different from the van der Waals structure (O2)2 detected experimentally. At its equilibrium geometry, the O4 molecule is a quasi-square (r(OO) ≈ 1.4 Å), slightly twisted out of plane, corresponding to the symmetry group D2d. The activation energy of the reaction O4(1Ag) → 202(X 3Σ- g) is found to be ≈ 15 kcal/mole, that of the inverse reaction, ≈ 75 kcal/mole. © 1980.
BibTeX:
@article{Adamantides1980,
  author = {Adamantides, V. and Neisius, D. and Verhaegen, G.},
  title = {Ab initio study of the O4 molecule},
  journal = {Chemical Physics},
  year = {1980},
  volume = {48},
  pages = {215-220},
  doi = {10.1016/0301-0104(80)80051-6}
}
Abstract: Nonrelativistic multiconfiguration Hartree–Fock wavefunctions and oscillator strengths are reported for selected transitions of neutral zinc and of its isoelectronic sequence up to W XLV. Correlation among the outer electrons has been considered in a detailed way. The final values, when compared with the few experimental observations or theoretical calculations available at the neutral end of the sequence, agree well with the most recent and accurate results published for Zn I. © 1980 IOP Publishing Ltd.
BibTeX:
@article{Biemont1980,
  author = {Biemont, E. and Godefroid, M.},
  title = {Outer correlation MCHF wavefunctions and oscillator strengths along the zinc isoelectronic sequence},
  journal = {Physica Scripta},
  year = {1980},
  volume = {22},
  pages = {231-239},
  doi = {10.1088/0031-8949/22/3/009}
}
Abstract: Accurate wavefunctions obtained by the MCHF method in its reduced form were used to compute the oscillator strengths for all possible electric dipole (E1) and electric quadrupole (E2) transitions between the states 11S, 21,3(S,P0), 31,3D and 41,3F 0 of helium-like systems ranging from He I to Ne IX. The length and velocity forms of the oscillator strengths are in close agreement in all cases; the correlation contributions to the gf values are discussed. The present results are the most accurate to date for E11,3(3D-4F0) and for all the E2 transitions.
BibTeX:
@article{Godefroid1980,
  author = {Godefroid, M. and Verhaegen, G.},
  title = {MCHF calculations of electric dipole and quadrupole oscillator strengths along the helium isoelectronic sequence},
  journal = {Journal of Physics B: Atomic and Molecular Physics},
  year = {1980},
  volume = {13},
  article number = {007},
  pages = {3081-3098},
  doi = {10.1088/0022-3700/13/16/007}
}
Abstract: SCF and CI calculations were carried out on the ground1 A′ state of HN3. The equilibrium geometry and vibration frequencies were computed. The results point to a planar structure (group Cs) but to a non-linear (170 °) N-N-N conformation. The calculated vibration frequencies are in fair agreement with experimental assignments. The dissociation path of the molecule to NH and N2 products was investigated and compared to the isoelectronic reaction of diazomethane. The dissociation energy of hydrazoic acid is estimated to be about -8 kcal/mole, with a potential barrier to dissociation of about 30 kcal/mole. © 1979 Springer-Verlag.
BibTeX:
@article{Lievin1979,
  author = {Lievin, J. and Breulet, J. and Verhaegen, G.},
  title = {Ab initio study of hydrazoic acid - I. The ground state: HN3(1 A′)},
  journal = {Theoretica Chimica Acta},
  year = {1979},
  volume = {52},
  pages = {75-88},
  doi = {10.1007/BF00581703}
}
Abstract: Transferable gaussian CH and CC bond functions and a C lone-pair function were optimized and compared to conventional polarization functions. The exponents (α) and position (γ,β) of these functions are α = 0.9, γ = 0.27 for CH bonds; α = 1.2, γ = 0.50 for CC bonds; α = 0.3, β = 0.47 for C lone-pair. © 1979.
BibTeX:
@article{Neisius1979,
  author = {Neisius, D. and Verhaegen, G.},
  title = {Bond functions for AB initio calculations on polyatomic molecules hydrocarbons},
  journal = {Chemical Physics Letters},
  year = {1979},
  volume = {66},
  pages = {358-362},
  doi = {10.1016/0009-2614(79)85034-4}
}
BibTeX:
@article{Godefroid1978,
  author = {Godefroid, M.},
  title = {An adaptation of acrz to calculate electric quadrupole oscillator strengths},
  journal = {Computer Physics Communications},
  year = {1978},
  volume = {15},
  pages = {275-282},
  doi = {10.1016/0010-4655(78)90097-8}
}
Abstract: A theoretical model is described which is based on the assumption that the temperature dependence of hyperfine coupling constants (h.c.c.s) in the E.S.R. spectra of organic free radicals is due to nuclear vibrations. The model is tested on the α-proton h.c.c.s of the methyl and hydroxymethyl radicals and in each case it shows that, although only the lowest vibrational mode contributes to the temperature dependence of the h.c.c.s, other modes do contribute to the vibrationally averaged coupling constant. © 1978 Taylor & Francis Group, LLC.
BibTeX:
@article{Sutcliffe1978,
  author = {Sutcliffe, B.T. and Gaze, C.},
  title = {A theoretical study of the temperature dependence of isotropic hyperfine coupling constants for the ch3 and ch2oh radicals},
  journal = {Molecular Physics},
  year = {1978},
  volume = {35},
  pages = {525-539},
  doi = {10.1080/00268977800100381}
}
Abstract: Large-basis-set calculations of near Hartree-Fock accuracy were performed on CO+(1σ-hole 2Σ+) and CO+)2σ-hole, 2Σ+); correlation energies for these systems and for CO were calculated using an atoms-in-molecule approach, relativistic energies and vibrational structure corrections were also considered. The results are: IP(CO, 1σ) = 542.4 (542.57) eV, IP(CO,2σ) = 297.0 (296.24) cV, Dc(CO, 1Σ+) = 10.8 (11.1) Ev, D3(CO+, 1σ, 2Σ+) = 11.9 eV, De(CO+, 2σ, 2Σ+) = 9.1 eV, where IP and De stand respectively for ionization potential and dissociation energy, and where the numbers in parentheses refer to the most recent experimental values. The electron transfers resulting from the ionization of inner-shell electrons are discussed. Finally a quantitative correlation is developed correlating absolute chemical shifts to charge densities. Agreement between the calculated values and those derived from the correlation is quite satisfactory. © 1977.
BibTeX:
@article{Corvilain-Berger1977,
  author = {Corvilain-Berger, S. and Verhaegen, G.},
  title = {Theoretical determination of the ionization potentials of the 1σ and 2σ electrons of CO(1Σ+)},
  journal = {Chemical Physics Letters},
  year = {1977},
  volume = {50},
  pages = {468-475},
  doi = {10.1016/0009-2614(77)80368-0}
}
Abstract: Three simplifying methodds are discussed and applied to the four lowest valence states of CH2(3B1, 1A1, 1B1 and 1Σ g+(1A 1*)) and to the two lowest of CH 2+(2A1 and 2∏u(2B1)). These methods concern: (1) the development of polarization functions for Gaussian‐lobe basis sets by least‐square fitting of numebrical multiconfigurational atomic fuinctions (this approach is tested also on (C2H2, (2) the use of intermediate Hamiltonians to calculate avoided crossings between potential hypersurfaces, and (3) thecalculation of correlation energies using an atoms‐in‐molecule approach. The calculated equilibrium geometries of the CH2 States are within 0.02 Å and 5° of available experimental data. The calculated term values and ionization potentials, Te(1A1 = 0.35 eV, Te (1B1) = 1.22 eV, Te (1Σ g+(1A 1*)) 2.48 eV, I.P. (2A1) = 10.39 eV and I. P. (2∏u(2B1)) = 10.58 eV, are in agreement with some recent theoretical studies, and are very close to existing experimental information. Copyright © 1977 John Wiley & Sons, Inc.
BibTeX:
@article{Gervy1977,
  author = {Gervy, D. and Verhaegen, G.},
  title = {Simplified methods for ab initio calculations. The valence states of CH2 and CH 2+},
  journal = {International Journal of Quantum Chemistry},
  year = {1977},
  volume = {12},
  pages = {115-131},
  doi = {10.1002/qua.560120111}
}
Abstract: Transition state Hamiltonians are used at a multiconflgurational level of accuracy to calculate the oscillator strength (length and velocity forms) of the 1s22s2(1S) → 1s22s2p(1P0) transition of beryllium. Three distinct approximations of the formalism are developed and examined. Copyright © 1977 John Wiley & Sons, Inc.
BibTeX:
@article{Godefroid1977,
  author = {Godefroid, M. and Berger, J.J. and Verhaegen, G.},
  title = {Multiconfigurational transition state calculations of atomic oscillator strengths. The resonance transition of beryllium},
  journal = {International Journal of Quantum Chemistry},
  year = {1977},
  volume = {12},
  pages = {119-123},
  doi = {10.1002/qua.560120817}
}
Abstract: In order to express precisely the abstract concept of symmetry, let us "work" on a common object-a tennis ball.
BibTeX:
@article{Herman1977,
  author = {Herman, M. and Lievin, J.},
  title = {Group theory: From common objects to molecules},
  journal = {Journal of Chemical Education},
  year = {1977},
  volume = {54},
  pages = {596-598}
}
Abstract: The least-energy dissociation path of the ground state of CH2N2 was determined from ab initio calculations using in a complementary way basis sets of minimal size (STO-3G) and double-zeta (DZ) quality. The results indicate that the least-energy point of attack of the N2 molecule on CH2 (1A1) is roughly perpendicular to the molecular plane (93 °), the C and N atoms being almost co-linear (angle C-N-N:203 ° with outermost N atom pointing away from CH2). The potential barrier of ∼ 1.2 eV found previously on the C2v dissociation path, disappears completely along the least-energy dissociation path (point group Cs (out-of-plane)). These findings corroborate the Woodward-Hoffman rules for this process since the outermost orbitals of the two intersecting states found in point group C2v (...2 b1 and ...8 a1) both correlate to the same irreducible representation (10 á) in point group Cs (out-of-plane). Larger basis set calculations (DZ + polarization functions on all centers, 3 dc and 3 dN developed here), were also carried out on CH2N2 (1A1,3A2 and1A2) at the1A1 equilibrium geometry and on CH2 (3B1) and N2 (1Σg+) at their respective equilibrium geometries. These calculations, together with consideration of correlation energy differences, yield D00 (CH2N2,1A1) = 19 kcal/mole and vertical excitation energies of 67 and 73 kcal/mole for the3A2 and1A2 states respectively. The latter value is in good agreement with the measured experimental value: 72.4 kcal/mole corresponding to the maximum of intensity in the1A2←1A1 absorption band. © 1977 Springer-Verlag.
BibTeX:
@article{Lievin1977,
  author = {Lievin, J. and Verhaegen, G.},
  title = {Theoretical study of the electronic structure of diazomethane - II. Determination of the least-energy dissociation path to CH2 and N2 products},
  journal = {Theoretica Chimica Acta},
  year = {1977},
  volume = {45},
  pages = {269-281},
  doi = {10.1007/BF00554536}
}
Abstract: A discussion is attempted of the validity of the Born-Oppenheimer approximation which is characterized as an asymptotic analysis leading to a semiclassical theory of molecular structure. It is suggested that there are inherent defects in the resulting semiclassical theory which will limit its utility in the explanation of highly accurate experiments involving molecules. © 1977.
BibTeX:
@article{Woolley1977,
  author = {Woolley, R.G. and Sutcliffe, B.T.},
  title = {Molecular structure and the born-Oppenheimer approximation},
  journal = {Chemical Physics Letters},
  year = {1977},
  volume = {45},
  pages = {393-398},
  doi = {10.1016/0009-2614(77)80298-4}
}
Abstract: Atomic oscillator strengths (length and velocity forms) are calculated for a series of transitions using transition Hamiltonians within the Hartree-Fock (HF) approximation. Two methods are implemented: the first defines a transition configuration (TC) corresponding to an average over the occupation numbers of initial and final configurations of the transition considered; the second defines a transition state (TS) corresponding to an average over the energies of the states involved in the transition. In general the TS results agree well with the corresponding HF values, while the TC results show larger discrepancies due to nonphysical self-interactions described in the text. An original method is described for obtaining a multiconfigurational transition state wavefunction. This method (MCTS) is applied to the evaluation of the oscillator strength of the transition Be(1s22s2 1S to 1s 22s2p1P degrees ).
BibTeX:
@article{Godefroid1976,
  author = {Godefroid, M. and Berger, J.J. and Verhaegen, G.},
  title = {A priori calculation of atomic oscillator strengths using correlated transition states},
  journal = {Journal of Physics B: Atomic and Molecular Physics},
  year = {1976},
  volume = {9},
  article number = {007},
  pages = {2181-2193},
  doi = {10.1088/0022-3700/9/13/007}
}
Abstract: Ab initio calculations of the dissociation process CH2N2 → CH2 + N2 are presented. Calculations were made on the ground 1A1 state as well as on the first few excited states (3B1, 1B1, 1A1*) necessary to the description of the dissociation mechanism in point group C2 v symmetry. The variation of energy was determined as a function of the parameters RCH-RNN and θHCH at several RCN values. Most results were obtained by using a basis set of Gaussian lobe functions contracted to "double-zeta" accuracy. A few calculations were made with the addition of polarization functions on all centers. The equilibrium geometry of the ground state, determined from coupled quadratic equations in the molecular parameters, is in satisfactory agreement with experimental values. The dissociation paths on the potential energy surfaces were determined. The locus of intersection points of the two 1A1 states is described; the avoided crossing of the two potential surfaces was determined from CI calculations based on an "intermediate" Hamiltonian. The geometric and electronic rearrangements due to dissociation as well as the bonding characteristics of the orbitals are discussed. The dissociation energy of the molecule (D00(CH2N2)) is calculated to be 0.91 eV. Finally, the term energy of the 1A1 state of CH2 is predicted to be 0.49 eV. © 1976 Springer-Verlag.
BibTeX:
@article{Lievin1976,
  author = {Lievin, J. and Verhaegen, G.},
  title = {Theoretical study of the electronic structure of diazomethane - I. The dissociation process CH2N2→CH2 + N2 in point group C2 v Symmetry},
  journal = {Theoretica Chimica Acta},
  year = {1976},
  volume = {42},
  pages = {47-65},
  doi = {10.1007/BF00548290}
}
Abstract: A computational study is made of the effect of basis set upon the energy, properties and inversion barrier of the phosphine molecule. The calculations are performed at both the SCF and CI level. The flexibility of the double zeta basis is discussed in the light of the results. © 1976 Springer-Verlag.
BibTeX:
@article{Scott1976,
  author = {Scott, J.M. and Sutcliffe, B.T.},
  title = {A configuration interaction study of phosphine using bonded functions},
  journal = {Theoretica Chimica Acta},
  year = {1976},
  volume = {41},
  pages = {141-148},
  doi = {10.1007/BF01178074}
}
Abstract: A method of forming the CI Hamiltonian matrix directly from a list of Bonded Functions and the MO-SCF wavefunction is proposed. For small expansions (circa 500 members) this method is definitely more efficient than the normal symbolic techniques and can be more efficient than iterative energy construction techniques. © 1975 Springer-Verlag.
BibTeX:
@article{Scott1975,
  author = {Scott, J.M. and Sutcliffe, B.T.},
  title = {Direct formation of the CI Hamiltonian matrix from an expansion of Bonded Functions},
  journal = {Theoretica Chimica Acta},
  year = {1975},
  volume = {39},
  pages = {289-300},
  doi = {10.1007/BF00551540}
}
Abstract: It is shown that in the LCAO-MO-MC-SCF problem, if the molecular orbital orthonormality constraints are introduced in the manner suggested by Kari and Sutcliffe or indeed by any similar method then the Hessian of the problem with respect to the linear coefficients is singular. The nature of this singularity is analysed and it is shown that in general it is possible to remove it in a level-shifting-like scheme, but that only in certain special cases is this procedure likely to be quickly convergent. © 1975 Springer-Verlag.
BibTeX:
@article{Sutcliffe1975,
  author = {Sutcliffe, B.T.},
  title = {The convergence properties of direct energy minimisation with respect to linear coefficients in the MC-LCAO-MO-SCF approach},
  journal = {Theoretica Chimica Acta},
  year = {1975},
  volume = {39},
  pages = {93-102},
  doi = {10.1007/BF00547789}
}
Abstract: The ionization potential of the BeH molecule is derived from a few Rydberg states observed in the absorption spectrum and from "ab initio" calculations of the energies of the ground states of the BeH and BeH+ molecules at their equilibrium distances. The values are in agreement and yield PI(BeH, X2Σ+) = 66 100 ± 500 cm-1. © 1974.
BibTeX:
@article{Colin1974,
  author = {Colin, R. and de Greef, D. and Goethals, P. and Verhaegen, G.},
  title = {The ionization potential of the BeH molecule},
  journal = {Chemical Physics Letters},
  year = {1974},
  volume = {25},
  pages = {70-73},
  doi = {10.1016/0009-2614(74)80334-9}
}
Abstract: A resumé of Boys' approach to configuration interaction calculations is presented, and a program suitable to perform such calculations is described in some detail. The results of a preliminary calculation on water, together with some timings are presented. © 1974 Springer-Verlag.
BibTeX:
@article{Diercksen1974,
  author = {Diercksen, G.H.F. and Sutcliffe, B.T.},
  title = {Configuration interaction by the method of bonded functions, some preliminary calculations},
  journal = {Theoretica Chimica Acta},
  year = {1974},
  volume = {34},
  pages = {105-114},
  doi = {10.1007/BF00551361}
}
Abstract: It is shown that in the LCAO-MO-SCF problem, if the molecular orbital orthonormality constraints are introduced in the manner first suggested by Fletcher, then the Hessian of the problem is singular. It is suggested that this singularity may well account for the slow convergence observed using direct energy minimization methods to solve the SCF problem. Ways of avoiding the consequences of this singularity are discussed. © 1974 Springer-Verlag.
BibTeX:
@article{Sutcliffe1974,
  author = {Sutcliffe, B.T.},
  title = {The convergence properties of direct methods of energy minimization with respect to linear coefficients in the LCAO-MO-SCF approach},
  journal = {Theoretica Chimica Acta},
  year = {1974},
  volume = {33},
  pages = {201-214},
  doi = {10.1007/BF00551255}
}
Abstract: Results of calculations using a configuration interaction LCAO-MO method are presented for the X 2Σ+ and A 2∏ states of BeH. Apart from the 1s shell of Be, the correlation energy of the remaining three electrons is calculated quantitatively using an extended basis set and complete configuration interaction including all single, double and triple replacements. The calculated spectroscopic constants are in excellent agreement with available experimental data. The present calculations also predict a value of De(BeH, X 2Σ+) = 2.115 eV, and dismiss the possibility of a potential maximum in the ground state potential energy curve.
BibTeX:
@article{Bagus1973,
  author = {Bagus, P.S. and Moser, C.M. and Goethals, P. and Verhaegen, G.},
  title = {Accurate ab initia calculation of the BeH molecule. I. the X 2Σ+ and A2∏ states},
  journal = {The Journal of Chemical Physics},
  year = {1973},
  volume = {58},
  pages = {1886-1897}
}
Abstract: The 1s‐ionization potentials of carbon and oxygen atoms have been calculated. The effects due to the relaxation of the valence orbitals have been taken into account at all levels of the calculations (Hartree‐Fock, relativistic, and correlation energies). The results obtained are IP(1s, C3P) = 295.2 eV and IP (1s, O3P) = 543.5 eV. Exchange‐induced splittings have also been determined: ΔE(C+, 1s(4P – 2P)) = 3.34 eV and ΔE(O +, 1s(4P – 2P)) = 4.43 eV. These predictions are compared to analogous experimental results. Copyright © 1973 John Wiley & Sons, Inc.
BibTeX:
@article{Corvilain1973,
  author = {Corvilain, S. and Verhaegen, G.},
  title = {K‐shell binding energies in C and O},
  journal = {International Journal of Quantum Chemistry},
  year = {1973},
  volume = {7},
  pages = {69-81},
  doi = {10.1002/qua.560070711}
}
Abstract: In this paper we obtain formulae useful in methods for the direct minimization of the energy functional in the LCAO‐MO‐MC‐SCF approach. The formulae are appropriate for dealing with variations in both the linear and nonlinear parameters. We include formulae for the usual closed‐ and open‐shell problems as special cases. Copyright © 1973 John Wiley & Sons, Inc.
BibTeX:
@article{Kari1973,
  author = {Kari, R. and Sutcliffe, B.T.},
  title = {Direct minimization of the energy functional in LCAO–MO calculations},
  journal = {International Journal of Quantum Chemistry},
  year = {1973},
  volume = {7},
  pages = {459-473},
  doi = {10.1002/qua.560070304}
}
Abstract: A study based on the INDO method has been made of a variety of σ radicals. The desirability of minimizing the energy with respect to molecular geometry for a number of small radicals (e.g., ·CONH2, H2C=N ·, H2C= ĊH) is discussed. INDO calculations have also been performed for a series of iminoxy radicals (R2C=NO·), the appropriate geometry around the radical center being chosen as that which minimizes the energy for the smallest radical in the series. An alternative method of determining the proportionality constants for relating esr hyperfine splittings to spin density matrix elements is suggested. Spin density distributions in the space around some of the radicals studied are expressed in the form of spin density contour maps.
BibTeX:
@article{Chiu1972,
  author = {Chiu, M.F. and Gilbert, B.C. and Sutcliffe, B.T.},
  title = {A Theoretical study of hyperfme coupling constants of some σ radicals based on the INDO method},
  journal = {Journal of Physical Chemistry},
  year = {1972},
  volume = {76},
  pages = {553-564}
}
Abstract: Ab initio calculations are performed on a serie of valence states of LiO. The calculations are carried out according to the LCAOMOSCF scheme with a basis set sufficiently large so as to furnish energies very close to the corresponding Hartree‐Fock limits. Correlation energies are calculated semi‐empirically using corresponding atomic data. The results are in good agreement with available experimental data concerning the equilibrium internuclear distance and vibration frequency of the ground state. A2 Π ‐ 2Σ+ electronic transition is predicted to lie in the infra‐red region of the spectrum at about 1750 cm−1. Copyright © 1972 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim
BibTeX:
@article{Liu1972,
  author = {Liu, H.P.D. and Verhaegen, G.},
  title = {Theoretical Calculation of the Electronic States of the Molecule LiO},
  journal = {Bulletin des Sociétés Chimiques Belges},
  year = {1972},
  volume = {81},
  pages = {109-124},
  doi = {10.1002/bscb.19720810109}
}
Abstract: Relativistic energies are computed for a series of j states corresponding to 1s22sm2pn (0?m?2; 0?n?6) configurations by solution of the hartree-fock-dirac equations. The j states calculated are those states whose eigenfunctions within a configuration correspond to a unique and maximum eigenvalue of the operator j2. In addition, average relativistic energies are obtained for all configurations considered. The two sets of results are compared, and in certain cases (for the 1s22p, 1s22p5, 1s22s22p, 1s 22s22p5 configurations) permit a determination of multiplet splittings (e(2p12/-2p 32/)). The results of these splittings are in excellent agreement with available experimental data. The present results also tend to confirm the assumption that the relativistic energy contributions for the j averaged ls states are the same for all states arising from the same configuration. This makes it possible to evaluate the relativistic energies of all states belonging to the configurations of interest to this paper. These in turn serve to re-evaluate more correctly recently obtained correlation energies for the same states.
BibTeX:
@article{Desclaux1971,
  author = {Desclaux, J.P. and Moser, C.M. and Verhaegen, G.},
  title = {Relativistic energies of excited states of atoms and ions of the second period},
  journal = {Journal of Physics B: Atomic and Molecular Physics},
  year = {1971},
  volume = {4},
  article number = {003},
  pages = {296-310},
  doi = {10.1088/0022-3700/4/3/003}
}
Abstract: Ab initio calculations (LCAO‐MO‐SCF) nearing Hartree‐Fock accuracy were made for a series of valence states of the molecules NH and OH+. The correlation energies of all states considered were calculated by a method used precedingly and described in this work. Good agreement with experimental data is found for a series of molecular properties such as equilibrium internuclear distances, term values, dissociation energies and ionization potentials; fair agreement is found for vibration frequencies and unharmonic constants. The precision of the present calculations allow definite predictions to be made concerning the relative energies of the singlet and triplet states in NH, and concerning the potential energy curves of unobserved singlets in OH+. Finally, the examination of the dissociation properties of the electronic states from calculations carried out at large internuclear distances, make it possible to reach conclusions concerning the eventual presence of potential maxima in their potential energy curves. Copyright © 1971 John Wiley & Sons, Inc.
BibTeX:
@article{Liu1971,
  author = {Liu, H.P.D. and Verhaegen, G.},
  title = {Electronic states of NH and OH+},
  journal = {International Journal of Quantum Chemistry},
  year = {1971},
  volume = {5},
  pages = {103-118},
  doi = {10.1002/qua.560050813}
}
Abstract: The Bethe-Goldstone formalism for calculating correlation energy has been applied to the 1s hole state in neon. The binding energy of the 1s electron is computed to be 870.0 eV which is in excellent agreement with experiment. © 1971.
BibTeX:
@article{Moser1971,
  author = {Moser, C.M. and Nesbet, R.K. and Verhaegen, G.},
  title = {A correlation energy calculation of the 1s hole state in neon},
  journal = {Chemical Physics Letters},
  year = {1971},
  volume = {12},
  pages = {230-232},
  doi = {10.1016/0009-2614(71)85052-2}
}
Abstract: The 1s and 2s electron binding energies in Ne are calculated from the Hartree-Fock and Fock-Dirac energies of Ne(1S0), Ne+(2S, 1s-hole) and Ne+ (2S, 2s-hole). Correlation energies are estimated from the work of Nesbet and of Oksüz and Sinanoǧlu. Close agreement with recent experimental data is found for both binding energies. © 1971.
BibTeX:
@article{Verhaegen1971,
  author = {Verhaegen, G. and Berger, J.J. and Desclaux, J.P. and Moser, C.M.},
  title = {A priori calculation of the 1s and 2s hole states in neon},
  journal = {Chemical Physics Letters},
  year = {1971},
  volume = {9},
  pages = {479-481},
  doi = {10.1016/0009-2614(71)80275-0}
}
Abstract: Using a generalised product wave function, an expression is given for the isotropic hyperfine coupling constant at a given atom in an aromatic π-radical. By a consistent scheme of approximation the expression is cast in a form in which the coupling constant at a given atom in the radical can be evaluated from the results of a Hückel calculation, provided that certain integrals are known. A scheme for assigning and relating these integrals is given, coupling constants are calculated for 13C, 14N, 17O and 19F atoms, and the calculations compared with experiment. © 1970 Springer-Verlag.
BibTeX:
@article{Chiu1970,
  author = {Chiu, M.F. and Sutcliffe, B.T.},
  title = {A semi-empirical approach to the estimation of ESR isotropic hyperfine coupling constants in aromatic radicals},
  journal = {Theoretica Chimica Acta},
  year = {1970},
  volume = {16},
  pages = {331-345},
  doi = {10.1007/BF00527081}
}
Abstract: In this paper we investigate the solution of the open-shell problem, in the LCAO approximation, for some first row atoms, by methods involving direct minimisation of the energy functional. We believe these methods to be applicable to the general multi-configuration SCF problem. © 1970.
BibTeX:
@article{Kari1970,
  author = {Kari, R. and Sutcliffe, B.T.},
  title = {Direct minimisation of the energy functional in some open-shell LCAO calculations on atoms},
  journal = {Chemical Physics Letters},
  year = {1970},
  volume = {7},
  pages = {149-152},
  doi = {10.1016/0009-2614(70)80271-8}
}
Abstract: Ab initio calculations (LCAO-MO-SCF) are performed on a series of valence levels of the molecules CH and NH+. Correlation energies are estimated semiempirically from corresponding atomic data. Close agreement with experiment is found for known states for a series of molecular properties such as equilibrium internuclear distances, vibration frequencies, term values, and dissociation energies. A low-lying 4∑- state in CH is calculated to lie 7500 cm-1 above the X 2∏ state. No observable quartet transition could be found for CH, while for NH+ a 4∏-4∑- transition should occur in the region of 1000 Å. Other qualitative differences in the observed spectra of the two molecules are discussed. Finally a value of D0 0(NH+)=3.4 eV is calculated.
BibTeX:
@article{Liu1970,
  author = {Liu, H.P.D. and Verhaegen, G.},
  title = {Electronic states of CH and NH+},
  journal = {The Journal of Chemical Physics},
  year = {1970},
  volume = {53},
  pages = {735-745}
}
Abstract: Hartree-Fock energies have been calculated for 333 valence states of atoms and ions of the second row of the periodic table corresponding to 1s 22sm2pn (m=0.1; 0<n<6) configurations. Multi-configuration Hartree-Fock energies were also calculated for 74 ground and excited states which may be described by wave functions of the type (a(1s 22s22pn)+b(1s22pn+2)). Relativistic contributions for the excited configurations were obtained approximately from computations of the relativistic energy of the 1s 22p6 1S0 and mately from computations of the relativistic energy of the 1s22p6 1S 0 and 1s22s22p6 1S 0 states. All the above calculations extend from the neutral atom up to Z=15 for the three-, four-, five- and six-electron series and up to Z=17 for the seven-, eight-, nine- and ten-electron series.
BibTeX:
@article{Verhaegen1970,
  author = {Verhaegen, G. and Moser, C.M.},
  title = {Hartree-Fock, correlation and term energies of valence excited states of atoms and ions of the second row of the periodic table},
  journal = {Journal of Physics B: Atomic and Molecular Physics},
  year = {1970},
  volume = {3},
  article number = {004},
  pages = {478-492},
  doi = {10.1088/0022-3700/3/4/004}
}
Abstract: The equilibrium vapor effusing from a Knudsen cell, in which solid ND 4Cl was evaporated, was analyzed by a quadrupole mass spectrometer. In the temperature range considered (335°-485°K) the main vaporization process corresponds to the decomposition of the solid towards gaseous ND 3 and DCl; the measured enthalpy change ΔH°407dec[ND4Cl(s)]=42.6±2.0 kcal mole-1 is very close to that measured for NE4Cl: ΔH°407dec[NH4Cl(s)]=42.5 kcal mole-1. Apart from the main gaseous species, small proportions (5×10-5-2×10 -3) of ND4Cl molecules were also observed. The ND 4Cl molecule fragments (>99%) under electron impact and yields the ND4+(m/e=22) ion. From the observed ion intensity ratios, as well as their dependence on temperature, D0°(NH 4Cl⇌NH3+HCl)= 10.0±3.0 kcal mole -1 was obtained confirming Clementi's computed prediction <14.0 kcal mole-1.
BibTeX:
@article{Goldfinger1969,
  author = {Goldfinger, P. and Verhaegen, G.},
  title = {Stability of the gaseous ammonium chloride molecule},
  journal = {The Journal of Chemical Physics},
  year = {1969},
  volume = {50},
  pages = {1467-1471}
}
Abstract: Results of ab initia calculations are presented for a series of valence levels of C2+ and for the two lowest states of Cs (x 1∑ g + and X′ IIu). Correlation energies of all the levels are estimated by a new scheme taking into account near-degeneracy effects in the molecule and in the constituent ion pairs. Results for C2 are in close agreement with experiment for equilibrium internuclear distances, vibration frequencies,, term energies and dissociation energies. For C 2 + the calculations show the ground state to be 4∑g - with relatively low-lying (∼0.6 eV)* δg and 2IIu levels. The electron-impact measurement for the appearance potential of C2 + is interpreted as C2 (3IIu, ν= 1)→ Cs+ (4∑-, ν=0). The quartet transition %→4∑- is predicted to lie at 60001. The major doublet transitions all lie in the infrared.
BibTeX:
@article{Verhaegen1968,
  author = {Verhaegen, G.},
  title = {Theoretical calculation of the electronic states of C2+},
  journal = {The Journal of Chemical Physics},
  year = {1968},
  volume = {49},
  pages = {4674-4679}
}
BibTeX:
@article{Csizmadia1967,
  author = {Csizmadia, I.G. and Harrison, M.C. and Moskowitz, J.W. and Sutcliffe, B.T.},
  title = {Non-empirical LCAO-MO-SCF-CI calculations on organic molecules with Graussian type functions},
  journal = {Theoretica Chimica Acta},
  year = {1967},
  volume = {7},
  pages = {156},
  doi = {10.1007/BF01151918}
}
Abstract: Matrix Hartree-Fock wave functions are calculated for the low-lying configurations of the BeS molecule The energy of each state is computed variationally and estimates made of differences in correlation energy between the various levels The results indicate a 1Σ+ ground state.
BibTeX:
@article{Verhaegen1967,
  author = {Verhaegen, G. and Richards, W.G.},
  title = {The ground state of the BeS molecule},
  journal = {Proceedings of the Physical Society},
  year = {1967},
  volume = {90},
  article number = {129},
  pages = {579-581},
  doi = {10.1088/0370-1328/90/2/129}
}
Abstract: The ground state and first excited state of the nitrogen-molecule positive ion are calculated using the matrix Hartree-Fock approximation, which results in a reversal of the observed spectroscopic order of states. The inclusion of estimates of correlation-energy differences between the levels corrects this and leads to a calculated term value of the excited state (1.17 eV) in extremely close agreement with experiment (1.16 eV).
BibTeX:
@article{Verhaegen1967b,
  author = {Verhaegen, G. and Richards, W.G. and Moser, C.M.},
  title = {Ground state and main spectroscopic system of the nitrogen-molecule positive ion},
  journal = {The Journal of Chemical Physics},
  year = {1967},
  volume = {47},
  pages = {2595-2598}
}
Abstract: Some low-lying valence levels of BN and C2 are calculated by the LCAO MO SCF method. Variational calculations are performed on three different configurations for BN and two for C2. Term values are obtained from the minima of the computed potential curves together with estimates of pair correlation energy differences between the various configurations. The results obtained for C2 are in reasonably good agreement (error∼0.2 eV) with experiment. For BN the calculations indicate a 3Π ground state with low-lying 3Σ+, 1Σ +, and 1Π states.
BibTeX:
@article{Verhaegen1967a,
  author = {Verhaegen, G. and Richards, W.G. and Moser, C.M.},
  title = {Low-lying valence levels of BN and C2. The ground state of BN},
  journal = {The Journal of Chemical Physics},
  year = {1967},
  volume = {46},
  pages = {160-164}
}
Abstract: This paper (Part I) describes the theoretical and computational bases of some non-empirical calculations on small organic molecules to be reported in later papers (Parts II et seq). Approximate solutions for the usual fixed nucleus electronic Hamiltonian, in the term of wave functions composed of Slater determinants, are discussed, with particular emphasis on their computational utility. Possible choices of basis functions, from which to form the determinants are examined, and the advantages of Gaussian type functions (GTF) centered on the component atoms are pointed out. Some of the properties of molecules which can be calculated using such approximate wave functions are outlined. Finally an attempt is made to discuss the current limitations of non-empirical calculations of the type described here, and some guesses are made about their future. Brief outlines as a set of appendices are given of the mathematical formalism and computational details of the calculations. © 1966 Springer-Verlag.
BibTeX:
@article{Csizmadia1966,
  author = {Csizmadia, I.G. and Harrison, M.C. and Moskowitz, J.W. and Sutcliffe, B.T.},
  title = {Non-empirical LCAO-MO-SCF-CI calculations on organic molecules with Gaussian type functions - Part I. Introductory review and mathematical formalism},
  journal = {Theoretica Chimica Acta},
  year = {1966},
  volume = {6},
  pages = {191-216},
  doi = {10.1007/BF00000001}
}
Abstract: Non-empirical molecular quantum chemical calculations were performed on formyl fluoride (HCOF) in the LCAO-MO-SCF framework using Gaussian type functions as atomic orbitals. In the first half of this paper a quantitative correlation has been established between some of the calculable molecular properties of HCOF and the size of the basis set used. It is hoped that the basic conclusions are general enough to be applicable to calculations of similar type on different molecules. The second part consists of a preliminary SCF study of HCOF in its electronic ground state. © 1966 Springer-Verlag.
BibTeX:
@article{Csizmadia1966a,
  author = {Csizmadia, I.G. and Harrison, M.C. and Sutcliffe, B.T.},
  title = {Non-empirical LCAO-MO-SCF-CI calculations on organic molecules with Gaussian type functions - Part II. Preliminary investigations on formyl fluoride},
  journal = {Theoretica Chimica Acta},
  year = {1966},
  volume = {6},
  pages = {217-239},
  doi = {10.1007/BF00000002}
}
BibTeX:
@article{Gilbert1966,
  author = {Gilbert, B.C. and Hanson, P. and Norman, R.O.C. and Sutcliffe, B.T.},
  title = {The cation-radical and the neutral radical from phenothiazine},
  journal = {Chemical Communications (London)},
  year = {1966},
  pages = {161-164},
  doi = {10.1039/C19660000161}
}
Abstract: Formulas are given for the spinless one- and two-particle density matrices and for certain other density functions in terms of bonded function wavefunctions.
BibTeX:
@article{Sutcliffe1966,
  author = {Sutcliffe, B.T.},
  title = {Matrix elements between bonded functions},
  journal = {The Journal of Chemical Physics},
  year = {1966},
  volume = {45},
  pages = {235-239}
}
Abstract: The low-lying valence levels of BeO, are calculated by the LCAO MO SCF method in order to ascertain the nature of the ground state of the molecule. Calculations of excited states using virtual orbitals are found to be inconclusive. Better results are found by doing variational calculations on three low-lying configurations for a series of internuclear distances, employing a large basis set and data on differences in molecular correlation energies between the various configurations. The calculations indicate a closed-shell 1∑+ ground state. Spectroscopic constants are derived for this and other valence states. An unobserved 3∑+- 3II transition is predicted to lie in the infrared region at about 9000 Å. The lowest-lying excited state is a 3II. This level is shown to lie sufficiently high with respect to the ground state so as not to require an alteration of the published dissociation energy.
BibTeX:
@article{Verhaegen1966,
  author = {Verhaegen, G. and Richards, W.G.},
  title = {Valence levels of beryllium oxide},
  journal = {The Journal of Chemical Physics},
  year = {1966},
  volume = {45},
  pages = {1828-1833}
}
Abstract: The evaporation of tin oxide SnO2 and mixtures of tin and tin oxide was studied. The vaporization reactions are (Equation Presented) The dissociation energy of the molecule SnO was determined: D°0 = 126.5±2.0 kcal/mole; as well as the polymerization energies ΔH 298° = 66.8±4, 136.5±5, 207.6±5 kcal/mole for (SnO)2, (SnO)3 snd (SnO)4 respectively. A re-interpretation of the total vapour pressures given in the literature was made. The presence of the polymeric molecules is the cause of previously unexplained differences.
BibTeX:
@article{Colin1965,
  author = {Colin, R. and Drowart, J. and Verhaegen, G.},
  title = {Mass-spectrometric study of the vaporization of tin oxides: Dissociation energy of SnO},
  journal = {Transactions of the Faraday Society},
  year = {1965},
  volume = {61},
  pages = {1364-1371}
}
Abstract: The mass spectrometric study of the vaporization of the compounds GeO 2(hex) and GeO(am) and of the mixture GeO2(hex)+Ge(c) made it possible to establish their mode of vaporization: GeO2(hex) →GeO(g)+1/2O2 (I) n GeO(am)→(GwO)n(g) (n = 1,2,3), (II) (n/2)GeO2(hex) + (n/2)Ge(c)→(GeO)n(g) (n = 1,2,3). (III) The enthalpies of vaporization are ΔH298° (I) = 124.3±2.4 kcal/mole; ΔH298°(II, n = 1) = 53.1± 1.0 kcal/mole; ΔH298°(III, n = 1) = 57.5±1.0 kcal/mole. The polymerization energies are ΔH 298° (GeO-GeO) = 44.7±3.0 kcal/mole; ΔH 298°(GeO-GeO-GeO) = 88.5±5.0 kcal/mole. Total pressures given in the literature were re-interpreted taking the presence of the polymers into account. The heat of formation of the metastable compound GeO(am) is ΔHf°(GeO) = -60.8±1.4 kcal/mole. The dissociation energy of the gaseous molecule GeO is D0°(GeO) = 156.2±1.9 kcal/mole.
BibTeX:
@article{Drowart1965,
  author = {Drowart, J. and Degreve, F. and Verhaegen, G. and Colin, R.},
  title = {Thermochemical study of the germanium oxides using a mass spectrometer: Dissociation energy of the molecule GeO},
  journal = {Transactions of the Faraday Society},
  year = {1965},
  volume = {61},
  pages = {1072-1085}
}
Abstract: The dissociation energy of the molecule ScO was determined: D 0°(ScO) = 160.9±3.5 kcal/mole. The dissociation energies of the molecules YO and LaO, D0°(YO) = 168.6±2.8 and D0°(LaO) = 191.0±2.5 kcal/mole, are discussed. The molecules SC2O, Y2O, Y2O2, La 2O, and La2O2 were identified. Their atomization energies are: D0°(Sc2O) = 245±11, D0° (Y2O) = 258±8, D0°(Y 2O2) = 445±12, D0° (La2O) = 266±8, D0° (La2O2) = 468±11 kcal/mole.
BibTeX:
@article{Smoes1965,
  author = {Smoes, S. and Drowart, J. and Verhaegen, G.},
  title = {Mass-Spectrometric Study of Gaseous Oxides and Suboxides of Scandium, Yttrium, and Lanthanum},
  journal = {The Journal of Chemical Physics},
  year = {1965},
  volume = {43},
  pages = {732-736}
}
Abstract: A number of gaseous ternary oxides have been identified by mass spectrometry, while vaporizing MgO, CaO, SrO and SnO2+Sn from Mo and W crucibles. The stabilities of the gaseous molecules SrMoO3, CaWO3, SrWO3, MgMoO4, CaMoO4, SrMoO4, MgWO4, CaWO4, SrWO4, SnWO4 and Sn2WO5, were deduced from the measurements.
BibTeX:
@article{Verhaegen1965,
  author = {Verhaegen, G. and Colln, R. and Exsteen, G. and Drowart, J.},
  title = {Mass spectrometric determination of the stability of gaseous molybdites, tungstites, molybdates and tungstates of magnesium, calcium, strontium and tin},
  journal = {Transactions of the Faraday Society},
  year = {1965},
  volume = {61},
  pages = {1372-1375}
}
Abstract: The dissociation energy of the molecules MgO, CaO, SrO was determined: D0°(MgO) = 86±5; D0°(CaO) = 93±5; D0(SrO) = 102±5 kcal/mole. The ground state was considered to be 1Σ. This choice is discussed. A discussion of the literature values for D0°(MgO, CaO, SrO) is made. The molecule Sr 2O was identified and its atomization energy determined: ΔH0°, at(Sr2O) = 194±6 kcal/mole.
BibTeX:
@article{Drowart1964,
  author = {Drowart, J. and Exsteen, G. and Verhaegen, G.},
  title = {Mass spectrometric determination of the dissociation energy of the molecules MgO, CaO, SrO and Sr2O},
  journal = {Transactions of the Faraday Society},
  year = {1964},
  volume = {60},
  pages = {1920-1933}
}
Abstract: The vaporization behavior of the systems boron-carbon and boron-carbon-silicon has been studied with a mass spectrometer. In addition to the gaseous species characteristic of graphite, silicon carbide and boron, the molecules BC2, B2C, BCSi, BSi2, BC, and BSi were identified and their atomization energies measured. The values are: 294, 254, 247, 174, 106, and 68 kcal/mole, respectively. The atomization energies of SiC, Si2C, and SiC2 have been redetermined.
BibTeX:
@article{Verhaegen1964,
  author = {Verhaegen, G. and Stafford, F.E. and Deowart, J.},
  title = {Mass spectrometric study of the systems boron-carbon and boron-carbon-silicon},
  journal = {The Journal of Chemical Physics},
  year = {1964},
  volume = {40},
  pages = {1622-1628}
}
Abstract: The ‘ spin polarization ’ induced in one part of a molecule by the presence of unpaired spins in another part is investigated in a general way, using a density matrix formulation. The general theory is then applied in a non-empirical calculation of spin densities and hyperfine coupling constants in the NH2 radical. © 1963 Taylor & Francis Group, LLC.
BibTeX:
@article{McWeeny1963,
  author = {McWeeny, R. and Sutcliffe, B.T.},
  title = {Spin polarization effects in paramagnetic molecules calculations on the nh2 radical},
  journal = {Molecular Physics},
  year = {1963},
  volume = {6},
  pages = {493-502},
  doi = {10.1080/00268976300100551}
}
Abstract: The unrestricted Hartree-Fock method in the LCAO-MO approximation is used to calculate the coupling constants for nitrogen and hydrogen in the NHa free radical. Both Slater and self-consistent field orbitals are used as basis functions. The effect of a spin annihilator after energy minimization, and the effects of "freezing" the nitrogen core are examined. The results are compared with those obtained in a recent configuration interaction calculation; and with the experimental results.
BibTeX:
@article{Sutcliffe1963,
  author = {Sutcliffe, B.T.},
  title = {Hyperfine electron spin resonance spectrum of the NH2 free radical},
  journal = {The Journal of Chemical Physics},
  year = {1963},
  volume = {39},
  pages = {3322-3326}
}
Abstract: Mass spectrometric technique has been employed to analyze the molecular beams effusing from mullite Knudsen cells containing Sn and alloys of Cu, Ag, and Au with Sn. From the experimental intensities of monatomic and diatomic species and the vapor pressure of Sn, the following dissociation energies are obtained: D 0° (Sn 2) = 45.8±4 kcal/mole, D 0° (AgSn) = 31.6±5 kcal/mole, D 0° (AuSn) = 57.5±4 kcal/mole, D 0° (CuSn) = 41.4±4 kcal/mole.
BibTeX:
@article{Ackerman1962,
  author = {Ackerman, M. and Drowart, J. and Stafford, F.E. and Verhaegen, G.},
  title = {Mass spectrometric study of the gaseous molecules above AgSn, AuSn, and CuSn alloys},
  journal = {The Journal of Chemical Physics},
  year = {1962},
  volume = {36},
  pages = {1557-1560}
}
Abstract: The molecules AuCr and AuPd have been identified. From data for the reaction Au 2+X=AuX+Au, and D 0°(Au 2) = 51.5 kcal/mole: D 0°(AuCr) = 50.4±3.5 kcal/mole, D 0°(AuPd) = 33.3±5 kcal/mole.
BibTeX:
@article{Ackerman1962a,
  author = {Ackerman, M. and Stafford, F.E. and Verhaegen, G.},
  title = {Studies of the vapors of the system Au-Cr and Au-Pd by mass spectrometry},
  journal = {The Journal of Chemical Physics},
  year = {1962},
  volume = {36},
  pages = {1560-1562}
}
BibTeX:
@article{Verhaegen1962,
  author = {Verhaegen, G. and Drowart, J.},
  title = {Mass spectrometric determination of the heat of sublimation of boron and of the dissociation energy of B2},
  journal = {The Journal of Chemical Physics},
  year = {1962},
  volume = {37},
  pages = {1367-1368}
}
Abstract: MOLECULES of high stability are known to exist in the vapours in equilibrium, with boron 1, carbon 2-5. silicon carbide 6,7and several metallic carbides and metal-carbon systems 8,9. It was therefore of interest to examine the vapour in equilibrium with the boron-carbon system. © 1962 Nature Publishing Group.
BibTeX:
@article{Verhaegen1962b,
  author = {Verhaegen, G. and Stafford, F.E. and Ackerman, M. and Drowart, J.},
  title = {Mass spectrometric investigation of gaseous species in the system boron-carbon},
  journal = {Nature},
  year = {1962},
  volume = {193},
  pages = {1280},
  doi = {10.1038/1931280a0}
}
Abstract: In this paper two correlations are proposed. The first correlation classifies the forty odd known homonuclear diatomic molecules according to the ratio α = ΔH 0 o (vap. M)/D 0 o(M 2) (heat of vaporization of an atom/dissociation energy of the diatomic molecule). Values of α = 0.5 to 1, 1.2 to 2.5 and >5 correspond to three categories each consisting of several whole groups of elements. The significance of this classification is discussed qualitatively. The second correlation shows that ΔH 0 o(vap. M) can be closely represented by Λ-BΣ iε i(M). Σ iε i(M) is the energy necessary to excite the atoms to a promoted " configuration " composed of equal contributions of a well-defined set of low lying electronic states of the free atom. Λ and B are empirical parameters. One set of electronic states is taken for Ca to Ni, Sr to Pd, and Ba to Pt with B = 1/2 and Λ = 178, 206, 250 kcal/g atom respectively; another set of electronic levels and Λ = 131 kcal and B = 1/4 represent ΔH 0 o(vap. M) for Ni, Cu, Zn, Pd, Ag, Cd, Pt, Au, Hg. Using the first classification, the experimental conditions are estimated for observation of the yet unknown homonuclear diatomic molecules of the transition elements. For this purpose a self-consistent set of free energy functions has been calculated.
BibTeX:
@article{Verhaegen1962a,
  author = {Verhaegen, G. and Stafford, F.E. and Goldfinger, P. and Ackerman, M.},
  title = {Correlation of dissociation energies of gaseous molecules and of heats of vaporization of solids. Part 1. - Homonuclear diatomic molecules},
  journal = {Transactions of the Faraday Society},
  year = {1962},
  volume = {58},
  pages = {1926-1938}
}

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Université Libre de Bruxelles – Faculté des Sciences