O (3P)+CH3SH reactions: Structures, energetics, and kinetics

The structures, barrier heights, reaction enthalpies, and thermal rate constants of four reaction paths involving hydrogen abstraction and addition processes between O and CH3SH were computed using the MollerPlesset perturbation theory at the second order level (MP2) and BB1K methods with the aug-cc-pV(T+d)Z basis set. A more accurate evaluation of the energetic of these reaction systems are performed by extrapolating the single point CCSD(T) energies to the complete basis set (CBS) limit approach using the BB1K and MP2/aug-cc-pV(T+d)Z geometries. The best estimates of the adiabatic barrier heights, determined using the CCSD(T)/CBS//(BB1K or MP2)/aug-cc-pV(T+d)Z method, are between 0.5 and 1.0 kcal mol-1 (R1, CH3S + OH), 5.3 and 5.5 kcal mol-1 (R2, CH2SH + OH), 1.3 and 2.3 kcal mol-1 (R3, CH3 + HSO), and 1.6 and 2.9 kcal mol-1 (R4, CH3SO + H). The thermal rate constants calculated using the dual-level direct dynamics by variational transition state theory with interpolated single-point energy corrections are in good agreement with experimental results. The calculated branching ratios at 300 K are 0.91:0.01:0.05:0.03 for the reactions paths R1R4, respectively, which indicate that hydrogen abstraction from the SH group is the main reaction path. (c) 2012 Wiley Periodicals, Inc.