Ab initio kinetic prediction of branching rate constants for reactions of H atoms with CH3O and CH2OH

The ground electronic state potential energy surfaces of the title reactions have been studied at the CCSD(T)/6-311 + G(3df, 2p) level of theory with the geometric parameters optimized at the CCSD/6-311 + G(3df, 2p) level of theory. The direct hydrogen abstraction channels and the indirect association/decomposition channels from the chemically activated methanol molecule have been considered. The barriers for the direct hydrogen abstraction processes in CH3O + H and CH2OH + H are predicted to be 0.11 and 2.2 kcal mol-1, respectively. The rate constants for decomposition of the internally excited CH3OH following the barrierless association reactions have been calculated by micro-canonical VTST/RRKM theory for all accessible product channels. The individual rate constants for the formation of CH2O + H2, predicted to occur primarily by the direct abstraction processes, are in good agreement with the available experimental data in the literature; however, the predicted total rate constants for both title reactions are much greater than those from the literature and CH3 + OH, instead of CH2O + H2, are concluded to be the major products of both processes, contrary to the assumption commonly made in the literature. The branching rate constants for all accessible product channels have been predicted for combustion modeling applications. Additionally, the rate constants for the two related reaction systems, CH3 + OH and CH2 + H2O, have been calculated and compared with the available experimental data; in both cases, agreement between theory and experiment is excellent.