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 X 2A′ and A 2A″ 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 X 2A′ and A 2A″ states calculated by perturbation theory are given. The calculated equilibrium geometries are: R e CH: 1.083 Å (X), 1.063 Å (A), R e CS: 1.573 Å (X), 1.557 Å (A) and α e HCS: 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 μ 0 (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.