The reaction mechanism of CH3SS with XO (X＝F, Cl, Br) have has been studied at MP2/6-311＋＋++G(d,p)//B3LYP/6-311＋＋++G (d, p) level. The breakage and formation of the chemical bonds in the main reaction channel have been discussed by the topological analysis method of electronic density. The calculated results shows that because of the low energy barrier and high exothermicity, the reaction of CH3SS with XO could occur easily in the atmosphere. Furthermore, the topological analysis shows that a four-membered- ring structure exists in the hydrogen abstract channel, it turns to a three-membered -ring structure by the a T-shaped structure, then the ring structure disappeared disappears and the products are gained.

Key words: topological analysis of electronic density, structure transition region, structure transition state