Jörg Senekowitsch

Theoretical rotational–vibrational spectrum of H2S

The high resolution rovibrational spectrum of H2S has been evaluated from three‐dimensional ab initio potential energy and electric dipole moment functions and variational rovibrational eigenfunctions, which took full account of anharmonicity effects and rotation–vibration coupling. The quality of the near equilibrium theoretical potential energy function has been checked by comparisons with experimental equilibrium structure, empirical quartic force fields, vibrational band origins, centrifugal distortion constants, and rotational energy levels. All parameters agree well with the available experimental data. Vibrational band intensities for the ν2, 2ν2, ν1, and ν3 bands have been calculated from empirical and ab initio dipole moment functions and compared with experimental and theoretical integrated band intensities. The difficulties arising by the derivation of such data from the experimental intensities of H2S are discussed. The theoretical results strongly suggest that higher than first derivatives ar...

Ab initio calculations of radiative transition probabilities in SH, SH+, and SH−

Potential energy and dipole moment functions for the ground states of SH, SH+, and SH− have been calculated from highly correlated electronic wave functions. The electric dipole moments in the vibrational ground states of 32SH, 32SH+, and 32SH− are calculated to be 0.74, 1.29, and 0.27 D, and the rotationless rates of spontaneous emission  A10 to be 1,  52, and 75 s−1, respectively. The predicted transition probabilities between the low lying vibrational states of the electronic ground state of SH and SD are among the smallest so far known for dipole allowed rotation‐vibration transitions. The calculated A–X transition probabilities in SH confirm recent indirect determinations of the radiative lifetimes and absorption oscillator strengths in the predissociating v’=0 level of the A state. The 4Σ− state is calculated to intersect the A 2Σ+ state at R=3.1 a.u., between the classical turning points of v’=0 and 1 in the A state.

On the bonding in doubly charged diatomics

SummaryThe potential energy of interacting atomic ions A++B+ often shows a shallow local minimum separated by a broad potential barrier from the dissociation products at much lower energy. Early interpretations of dication potential shapes were based on the similarity of the electronic structure between isoelectronic neutral and ionic species and led to a picture of a chemical bond superimposed on a repulsive Coulomb potential. More recently, barriers in dication potentials have commonly been interpreted as avoided curve crossings involving covalent and ionic structures. In this paper, we demonstrate that the former model is the appropriate one except in cases with very small asymptotic ionic/covalent energy splittings. By deriving dication wavefunctions from their neutral isoelectronic counterparts, we obtain upper bound dication potential curves which show all the characteristic features. By further modeling induction effects, we arrive at an almost quantitative fit of accurateab initio dication potentials. The “chemical bond plus electrostatic repulsion’ interpretation of dication interactions also explains why the accurate calculation of potential curves appears to be much more demanding for dications than for isoelectronic neutrals.

Metastable 3Σ−g ground state of F++2 and the bonding in molecular dications

Large multireference configuration interaction (MR‐CI) calculations on the F++2 ion predict a 3Σ−g ground state, metastable with respect to tunneling into the F++F+ nuclear continuum. The potential energy curve displays a 0.40 eV barrier at Rb=1.607 A, between the local potential minimum (Re=1.289 A) and the 3Pg(F+)+3Pg(F+) asymptote at 7.69 eV lower energy. The potential barrier traps four quasibound vibrational levels, with a tunneling lifetime of 16 ms for v=0. A Dunham analysis at the well minimum gives ωe=919.4 cm−1, ωexe=16.31 cm−1, Be=1.073 cm−1, and αe=0.0316 cm−1. In a departure from an earlier viewpoint, the origin of the barrier in this and other dications is interpreted as a sum of the e2/R Coulomb repulsion and the ordinary chemical bonding of the constituent ions. This model also explains the purely repulsive character found for the valence‐excited 1Δg and 1Σ+g states.

An accurate potential energy function of the H2− ion at large internuclear distances

Abstract A multireference configuration interaction approach has been used to calculate the potential energy function of the H 2 − ion for R ⩾ 3.0

Potential energy and dipole moment functions of the HCS radical

Abstract The three-dimensional MCSCF CI potential energy, electric dipole and electronic transition moment functions have been calculated for the X2A′ and A2A″ electronic states of the HCS radical. These states adiabatically correlate with the two components of a 2Π electronic state for linear configurations and their ro-vibronic spectra exhibit the Renner-Teller effect. Such spectra have been evaluated from variational ro-vibronic wavefunctions, which take into account both anharmonicity effects and rotation-vibration coupling. The nuclear and electronic angular momentum couplings have also been considered. Spectroscopic constants for the X2A′ and A2A″ states calculated by perturbation theory are given. The calculated equilibrium geometries are: ReCH: 1.083 A (X), 1.063 A (A), ReCS: 1.573 A (X), 1.557 A (A) and αeHCS: 131.8° (X), 180° (A), respectively. The electronic barrier to linearity in the electronic ground state is calculated to be 3063 ± 200 cm−1. The fundamental vibrational band origins and intensities (at 300 K) in the electronic ground state of HCS are predicted to be: 3104 cm−1/6 cm−2 atm−1 (CH stretch), 1165 cm−1/43cm−2 atm−1 (CS stretch) and 871 cm−1/54 cm−2 atm−1 (bend). The fundamental frequencies are expected to be accurate to within about 30 cm−1, the vibrational intensities to within about 10 to 20%. The electric dipole moment μ0 (X) is calculated to be 0.85 ± 0.05 D. The K-reordering due to the electronic angular momentum coupling is discussed. Absolute line intensities (up to J″ = 9) have been calculated and are given for a few intense lines.

Ab initio calculation of spectroscopic properties for the HLiH− ion in the X 1Σ+g state

Near equilibrium three‐dimensional potential energy and electric dipole moment surfaces of the bound negative ion HLiH− were calculated from highly correlated CEPA electronic wave functions. The HLiH− ion is linear with Re=1.743 A. From the potential energy surface the anharmonic vibration–rotation term values were calculated variationally and by perturbation theory. The fundamental vibrational transitions in HLiH− are predicted to lie at ν1(J=0)=1014 cm−1, ν2(J=1)=429 cm−1, ν3(J=0)=1079 cm−1. The D0 dissociation energy relative to the LiH+H− asymptote is calculated to be 2.34 eV, the vertical electron detachment energy to be 3.10 eV. The components of the electric dipole moment surface are given analytically.

CALCULATED ROTATIONAL AND ROVIBRATIONAL SPECTRA OF D2S AND HDS

Rovibrational energy levels, transition frequencies, and linestrengths are computed variationally for the sulfur hydrides D2S and HDS, using ab initio potential energy and dipole surfaces. Wave-numbers for the pure rotational transitions agree to within 0.2 cm−1 of the experimental lines. For the fundamental vibrational transitions, the band origins for D2S are 860.4, 1900.6, and 1912.0 cm−1 for ν2, ν1, and ν3, respectively, compared with the corresponding experimental values of 855.4, 1896.4, and 1910.2 cm−1. For HDS, we compute ν2 to be 1039.4 cm−1, compared with the experimental value of 1032.7 cm−1. The relative merits of local and normal mode descriptions for the overtone stretching band origins are discussed. Our results confirm the local mode nature of the H2S, D2S, and HDS system.

Spin‐forbidden decay of the dication HS2+

The lifetimes of the low‐lying vibrational levels of the X2Π state of the recently identified dication HS2+ [Miller et al., Int. J. Mass Spectrom. Ion Proc. 100, 505 (1990)] are considered. The stability of this state is attributable to a barrier formed from the avoided crossing of 2Π states asymptotically characterized as H++S+ and H+S2+. As a result of this barrier, the nonrelativistic X2Π potential energy curve supports several quasibound vibrational levels that are long lived with respect to tunneling. However, this is not the principal decay mechanism. We show that the lifetimes of the low‐lying vibrational levels, v=0−4, are controlled entirely by the spin–orbit induced perturbation, 14Σ−∼X2Π, and the corresponding allowed crossing of the X2Π potential energy curve by the dissociative 14Σ− potential energy curve which correlates with the ground state asymptote H++S+(4S).

Theoretical calculations of the vibrational transition probabilities in hydrogen selenide

Abstract Three-dimensional ab initio dipole and potential energy functions for H 2 Se have been calculated from highly correlated SCEP CEPA wavefunctions. First-order relativistic corrections according to the Cowan-Griffin approach, which retains only the mass velocity and one-electron Darwin terms, have been applied. These data have been used in perturbation and variational calculations of anharmonic vibration-rotation term values and wavefunctions. Radiative transition probabilities between vibrational levels up to about 10000 cm −1 have been calculated from electric dipole transition matrix elements. It is found that the radiative lifetimes vary in a mode-specific way.