A computational study on the mechanism and kinetics of the reaction between CH3CH2S and OH

Abstract

The reaction mechanism of CH₃CH₂S with OH radicals is studied at the CBS-QB3 level of theory. Five substitution processes and eleven addition–elimination channels are identified for the title reaction. The calculated results indicate that addition–elimination channels CH₃CHS + H₂O, CH₂CH₂ + HSOH, CH₃CHSO + H₂ and CH₃CH₂SH + O are dominant. Other channels may be negligible due to the high barrier heights. Rate constants and branching ratios are estimated by means of the conventional transition state theory with zero curvature tunnelling over the temperature range of 200–3000 K. The calculation shows that the overall rate constant in the temperature of 200–3000 K is mainly dependent on the channels CH₃CHS + H₂O, CH₂CH₂ + HSOH and CH₃CH₂SH + O. The three-parameter expression for the total rate constant is fitted to be k_total = 7.42 × 10⁻²¹T^2.63 exp(−772.43/T) cm³ molecule⁻¹ s⁻¹ between 200–3000 K.