Direct ab initio dynamics calculation of the reaction rates of CH ₃OCl with OH

A direct ab initio dynamics method was carried out for the reaction CH ₃OCI + OH → products. Three abstraction channels from chlorine atom, in-plane hydrogen, and out-of-plane hydrogen atoms at the CH₃ group have been found. The optimized geometries and frequencies of the stationary points and the minimum-energy paths (MEPs) were calculated at the MP2/6-311G(d,p) level. To improve the reaction enthalpy and potential barrier, single-point calculations were made at three higher levels of theory, the approximate QCISD-(T)/6-311++G(3df,2pd), G3, and G3(MP2) levels. Furthermore, the rate constants for three abstraction channels were evaluated using canonical variational transition state theory (CVT) with the small-curvature tunneling correction (SCT) over a wide temperature range of 220-2000 K at above three higher theory levels, respectively. The calculated rate constants as well as branching rates are in reasonable agreement with the experimental values in the temperature region 250-341 K. The present results indicate H-abstraction especially from out-of-plane hydrogen is the main reaction pathway, while Cl-abstraction is much less competitive.