Theoretical study of the ground and first excited singlet state potential energy surfaces of disulphur monoxide (S2O)

An extended region of the ground state potential energy surface (PES) in the vicinity of the experimentally observed isomer of disulphur monoxide (S2O) has been characterized using second-order generalized Van Vleck perturbation theory (GVVPT2) and the cc-pVDZ basis set. The corresponding region of the PES of the first excited singlet state, [Ctilde] 1A′, was analysed in order to elucidate the nature of the experimentally observed dissociation of the excited state S2O. Our calculations support experimental results suggesting the existence of several quasi-bound vibrational energy levels on the excited state PES. The second excited singlet state, [Dtilde] 1A′, was also examined. Our results corroborate the hypothesis that the cause of the predissociation of excited state S2O into its ground state dissociation products is due to the interaction of the lowest two excited state PESs at elongated S-S bond distances. Additional GVVPT2 calculations for the ground and excited state equilibrium structures were performed with the cc-pVTZ basis, and are in good agreement with experimental and CI results.