A CASSCF/CASPT2 study on the low‐lying electronic states of the CH 3 SS and its cation

Complete active space self‐consistent field (CASSCF) and multiconfiguration second‐order perturbation theory (CASPT2) calculations with contracted ANO‐RCC basis set were performed for low‐lying electronic states of CH 3 SS and its cation in C s symmetry. For the ground state X 2 A″ of CH 3 SS, the calculated S‐S stretching mode is in good agreement with experimental reports. The electron transitions of CH 3 SS + , X 1 A′ → 1 1 A″, X 1 A′ → 2 1 A′, and X 1 A′ → 2 1 A″, are predicted at 1.055, 3.247, and 3.841 eV. Moreover, the calculated adiabatic and vertical ionization potential and adiabatic affinity are in reasonable agreement with the experimental data. The CASSCF/CASPT2 potential energy curves (PECs) were calculated for S 2 ‐loss dissociation from the X 2 A″, 1 2 A′, and 2 2 A″ states. The electronic states of the CH 3 radical and S 2 molecule as the dissociation products were carefully determined by checking energies and geometries of the asymptote products. The S 2 ‐loss PEC for CH 3 SS indicate that S 2 ‐loss dissociation occurs from the X 2 A″ state leading to CH 3 (1 2 A″) + S 2 (X 3 Σ   g − ), the 1 2 A′ and 2 2 A″ leading to CH 3 (1 2 A″) + S 2 ( 1 Δ g ). © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012.