Theoretical study on predissociation of B³Σ_u^- of sulfur dimer

A high level ab initio study on electronic states of sulfur dimer S₂ is carried out by utilizing multi-reference configuration interaction plus Davidson correction (MRCI+Q) method. The modification to the electronic structures caused by spin-orbit coupling (SOC) effect is taken into consideration by the state-interacting method with the full Breit-Pauli Hamiltonian. The potential energy curves (PECs) of 19 Λ-S states and 52 Ω states generated from the Λ-S states are calculated. With the aid of calculated SOC matrix elements and the PECs of the Ω states, we discuss the predissociaiton of the B³Σ_u^- state. The variation of line width of B³Σ_u^-- X³Σ_g^- transitions with vibrational quantum number v' of the B³Σ_u^- are determined from Fermi golden rule calculations. Our study indicate that the predissociation of the B³Σ_u^- state is induced by the strong spin-orbit coupling with different electronic excited states, resulting in the abnormal dependence of the dissociation rate on vibrational states.