Spin-orbit ab initio study of the S 2 (B 3 Σ - u →X 3 Σ - g (ν′≥18,0)) diffuse bands

The diffuse bands B ３ Σ - u →X ３ Σ - g (ν′≥18,0) of diatomic molecule S 2 observed in the experiment are investigated. The electronic potential curves,including the spin-orbit coupling (SOC) effect of B ３ Σ - u and repulsive 1 ５ Π u ， 2 3 Σ + u states are calculated. For the diffuse bands beginning at (18,0), a point of view different from others' results is presented in this work. Our results indicate that the SOC induced predissociation between B ３ Σ - u and 1 ５ Π u ， 2 3 Σ + u plays the key role in the diffusion of spectra. Comparison with experimental results shows good agreement.