Ab initio calculations on SCl₂and low-lying cationic states of SCl₂⁺Franck-Condon simulation of the UV photoelectron spectrum of SCl₂

Geometry optimization calculations were carried out on the X̃1A1state of SCl2and the X̃2B1, Ã2B2, B̃2A1, c̃2A1, D̃2A2, and Ẽ2B2states of SCl2+at the restricted-spin coupled-cluster single-double plus perturbative triple excitation [RCCSD(T)] level with basis sets of up to the augmented correlation-consistent polarized quintuple-zeta [aug-cc-pV(5+d)Z] quality. Effects of core electron correlation, basis set extension to the complete basis set limit, and relativistic contributions on computed minimum-energy geometrical parameters and/or relative electronic energies were also investigated. RCCSD(T) potential energy functions (PEFs) were calculated for the X̃1A1state of SCl2and the low-lying states of SCl2listed above employing the aug-cc-pV(5+d)Z basis set. Anharmonic vibrational wave functions of these neutral and cationic states of SCl2, and Franck-Condon (FC) factors of the lowest four one-electron allowed neutral photoionizations were computed employing the RCCSD(T)/aug-cc-pV(5+d)Z PEFs. Calculated FC factors with allowance for the Duschinsky rotation and anharmonicity were used to simulate the first four photoelectron (PE) bands of SCl2. The agreement between simulated and observed He I PE spectra reported by Colton et al. [J. Electron Spectrosc. Relat. Phenom. 3, 345 (1974)] and Solouki et al. [Chem. Phys. Lett. 26, 20 (1974)] is excellent. However, our FC spectral simulations indicate that the first observed vibrational component in the first PE band of SCl2is a "hot" band arising from the SCl2+X̃2B1(0, 0 0)←SCl2+X̃1A1(1, 0, 0) ionization. Consequently, the experimental adiabatic ionization energy of SCl2is revised to 9.55±0.01 eV, in excellent agreement with results obtained from state-of-the-art ab initio calculations in this work.