LAUSR

Abstract This work presents the mechanism and chemical kinetics for the CH3SH + OH reaction in a broad condition range (200–2000 K & 0.76–760,000 Torr) using the CCSD(T)/aug-cc-pV(T,Q)Z//M06-2X/aug-cc-pV(T+d)Z and Rice–Ramsperger–Kassel–Marcus based master equation (RRKM-ME) calculations. The treatments of the hindered internal rotor (HIR) and tunneling effects were taken into account. The good agreement between our calculated rate constants and experimental values resolves the previous discrepancy between experiment and theory. The reaction mechanism is revealed in detail as: (i) the H-abstraction channel from the thiol (-SH) group is more thermodynamically and kinetically favorable than from the methyl (-CH3) group; (ii) U-shaped temperature-dependent behaviors and weakly positive pressure-dependence at low temperature (T ≤ 500 K) of the rate constants are observed; and (iii) both HIR and tunneling corrections play a role in obtaining reliable rate constants. Besides, the performance of selected chemical quantum methods (i.e., M06-2X, BH&HLYP, B3LYP, and MP2) on the calculated rate constants was examined thoroughly. Furthermore, it is predicted that CH3SH is not a persistent organic pollutant due to its short atmospheric lifetime (~5 h) due to OH radicals and its products (CH2SH and CH3S) can photolyze under the sunlight.