Computational study on the reaction of CH3SCH2CH3 with OH radical: mechanism and enthalpy of formation

The reaction mechanism of CH3SCH2CH3 with OH radical is studied at the CCSD(T)/6-311+G(3df, p)//MP2/6-31+G(2d, p) level of theory. Three hydrogen abstraction channels, one substitution process and five addition-elimination channels are identified in the title reaction. The result shows hydrogen abstraction is dominant. Substitution process and addition-elimination reactions may be negligible because of the high barrier heights. Enthalpies of formation [Delta H-f((298.15K))o] of the reactants and products are evaluated at the CBS-QB3, G3 and G3MP2 levels of theory, respectively. It is found that the calculated enthalpies of formation by the aforementioned three methods are in consistent with the available experimental data. Rate constants and branching ratios are estimated by means of the conventional transition state theory with the Wigner tunneling correction over the temperature range of 200-900 K. The calculation shows that the formations of P1 (CH2SCH2CH3 + H2O) and P2 (CH3SCHCH3 + H2O) are major products during 200-900 K. The three-parameter expressions for the total rate constant is fitted to be ktotal 1.45 x 10(-21)T(3.24) exp(-1384.54/T) cm(3) molecule(-1) s(-1) from 200 to 900 K.