Kinetics investigation of the hydrogen abstraction reaction between CH3SS and CN radicals

The reaction mechanisms and rates for the H abstraction reactions between CH3SS and CN radicals in the gas phase were investigated with density functional theory (DFT) methods. The geometries, harmonic vibrational frequencies, and energies of all stationary points were obtained at B3PW91/6-311G(d,p) level of theory. Relationships between the reactants, intermediates, transition states and products were confirmed, with the frequency and the intrinsic reaction coordinate (IRC) analysis at the same theoretical level. High accurate energy information was provided by the G3(MP2) method combined with the standard statistical thermodynamics. Gibbs free energies at 298.15K for all of the reaction steps were reported, and were used to describe the profile diagrams of the potential energy surface. The rate constants were evaluated with both the classical transition state theory and the canonical variational transition state theory, in which the small-curvature tunneling correction was included. A total number of 9 intermediates (IMs) and 17 transition states (TSs) were obtained. It is shown that IM1 is the most stable intermediate by the largest energy release, and the channel of CH3SS + CN -> IM3 -> TS10 -> P1(CH2SS + HCN) is the dominant reaction with the lowest energy barrier of 144.7 kJ mol(-1). The fitted Arrhenius expressions of the calculated CVT/SCT rate constants for the rate-determining step of the favorable channel is k = 7.73x106T (1.40)exp(-14,423.8/T)s(-1) in the temperature range of 200-2000 K. The apparent activation energy E-a(app.) for the main channel is -102.5 kJ mol(-1), which is comparable with the G3(MP2) energy barrier of -91.8 kJ mol(-1) of TS10 (relative to the reactants).