On the kinetic mechanism of the hydrogen and oxygen abstraction reactions of CH3S with HOO: A dual-level direct dynamics study

The hydrogen and oxygen abstraction mechanism for the radical–radical reaction of CH3S with HOO has been investigated at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-311+G(d,p) level of theory on both the singlet and triplet potential energy profiles. Four hydrogen abstraction channels and one oxygen abstraction process are found for the title reaction. The calculations indicate that the triplet potential energy profile is much lower than the singlet energetically. Two hydrogen abstraction channels Rc, Rd and one oxygen abstraction process Re are identified on the triplet potential energy profile. Channel Rc, formation of CH3SH + 3O2, is the most favorable. Furthermore, the rate constants of channel Rc in a temperature range 200–800 K are calculated by means of the canonical variational transition state theory with small-curvature tunneling correction. The fitted three-parameter expression for kCVT/SCT of the major pathway is kCVT/SCT = 2.80 × 10−39T7.49exp(6071/T) cm3 molecule−1 s−1 and it shows a negative dependence in the calculated temperature range.