Ab initio study of molecular vibrations in the X2Σ+, A2Π, B2Σ+, and C2Σ+ states of CS+ and the vibrational structure in the photoelectron spectrum of CS

Molecular vibrations in the X2Σ+, A2Π, B2Σ+, and C2Σ+ states of CS+ are studied by ab initio calculations using accurate potential energies. The calculated ωe and ωexe values for the B2Σ+ state bear out the emission spectroscopy values of Tsuji et al. as more accurate than another emission spectroscopy values. The C2Σ+ state is found to have a double potential well. Our value of ωe for its inner-well is 46 cm−1 larger than the photoelectron (PE) spectroscopy value. The discrepancy might be partly due to the experimental determination of ωe from only the observed PE spectrum because of an insufficient number of inner-well vibrational states involved in the anharmonicity of vibration. Based on theoretical intensity distributions in the vibrational structures for the PE bands of CS, the vibrational components of the fourth band in the observed PE spectrum are interpreted.