Computational study of the reactions of methanol with the hydroperoxyl and methyl radicals

The reactions of CH₃OH with the HO₂ and CH₃ radicals are important in the combustion of methanol and are protoypes for reactions of heavier alcohols in biofuels. In this study, the thermochemistry and barrier heights for these reaction systems are computed with CCSD(T) theory extrapolated to the complete basis set limit. These properties are further refined by including a full treatment of the connected triple excitations, a second-order perturbative treatment of quadruple excitations, core-valence corrections, and scalar relativistic effects. It is shown that the M08-HX and M08-SO hybrid meta-GGA density functionals can achieve sub-kcal mol^-1 agreement with the high-level ab initio results. The thermal rate constants for the methanol reactions are calculated with these density functionals by direct dynamics at the level of variational transition state theory with a curvilinear dividing surface and multidimensional tunneling. This work was supported in part by the U. S. Department of Energy.