The reaction mechanism of CH3SH with NO2 was investigated by using the density functional theory. The optimum geometries and frequencies of the reactants, transition states and products were computed at the B3LYP/6-311＋＋G(d,p) level of theory. Stationary points of the reaction channels were confirmed by the vibration analysis and the intrinsic reaction coordinate (IRC) tracing. The species energies at all stationary points were corrected by single-point calculations at the G3B3 and CCSD(T)/6-311＋＋G(d,p) levels. The rate constants of the reactions were evaluated by means of the classical transition state theory and the canonical variational transition state theory in which the small-curvature tunneling correction was included. Five possible reaction channels have been identified for the title reaction. Based on the potential energy surface and the kinetics, it can be concluded that the major reaction channel is the hydrogen abstraction of SH by N atom of NO2, leading to the formation of CH3S and HNO2. In the temperature range of 200～3000 K, the overall rate constants are of positive temperature dependence, and the rate constant of channel R→TS1→P1 can be described by the expression as k1CVT/SCT＝1.93×10－16T0.21exp(－558.2/T) cm3•molecule－1•s－1.

Key words: CH₃SH, NO₂, reaction mechanism, rate constant