Theoretical rate coefficients for the reaction of methyl radical with hydroperoxyl radical and for methylhydroperoxide decomposition

The kinetics of the CH3 + HO2 bimolecular reaction and the thermal decomposition of CH3OOH are studied theoretically. Direct variable reaction coordinate transition state theory (VRC-TST), coupled with high level multireference electronic structure calculations, is used to compute capture rates for the CH3 + HO2 reaction and to characterize the transition state of the barrierless CH3O + OH product channel. The CH2O + H2O product channel and the CH3 + HO2 → CH4 + O2 reaction are treated using variational transition state theory and the harmonic oscillator and rigid rotor approximations. Pressure dependence and product branching in the bimolecular and decomposition reactions are modeled using master equation simulations. The predicted rate coefficients for the major products channels of the bimolecular reaction, CH3O + OH and CH4 + O2, are found to be in excellent agreement with values obtained in two recent modeling studies. The present calculations are also used to obtain rate coefficients for the CH3O + OH association/decomposition reaction.