Theoretical studies on the reactions CH₃SCH₃ with OH, CF₃, and CH₃ radicals

The multiple-channel reactions OH + CH₃SCH₃ → products, CF₃ + CH₃SCH₃ → products, and CH₃ + CH₃SCH₃ → products are investigated by direct dynamics method. The optimized geometries, frequencies, and minimum energy path are all obtained at the MP2/6-31+G(d,p) level, and energetic information is further refined by the MC-QCISD (single-point) method. The rate constants for eight reaction channels are calculated by the improved canonical variational transition state theory with small-curvature tunneling contribution over the temperature range 200-3000 K. The total rate constants are in good agreement with the available experimental data and the three-parameter expressions k₁ = 4.73 × 10^-16T^1.89 exp(-662.45/T), k₂ = 1.02 × 10^-32T^6.04 exp(933.36/T), k₃ = 3.98 × 10^-35T^6.60 exp(660.58/T) (in unit of cm³ molecule^-1 s^-1) over the temperature range of 200-3000 K are given. Our calculations indicate that hydrogen abstraction channels are the major channels and the others are minor channels over the whole temperature range.