Ab initio/DFT theory and multichannel RRKM study on the mechanisms and kinetics for the CH3SÂ +Â CO reaction

The potential energy surface for the reaction of CH3S with CO was calculated at the G3MP2//B3LYP/6-311++G(d,p) level. The rate constants for feasible channels leading to several products were calculated by TST and multichannel-RRKM theory. The results show that addition-elimination mechanism is dominant, while hydrogen abstraction mechanism is uncompetitive. The major channel is the addition of CO to CH3S leading to an intermediate CH3SCO which then decomposes to CH3 + OCS. In the temperature range of 200-3000 K, the overall rate constants are positive temperature dependence and pressure independence, and it can be described by the expression as k = 1.10 × 10−16T1.57exp(−3359/T) cm3 molecule−1 s−1. At temperature between 208 and 295 K, the calculated rate constants are in good agreement with the experimental upper limit data. At T = 1000 and 2000 K, the major product is CH3 + OCS at lower pressure; while at higher pressure, the stabilization of IM1 is dominant channel.