Master equation modeling of the unimolecular decompositions of hydroxymethyl (CH2OH) and methoxy (CH3O) radicals to formaldehyde (CH2O) + H.

α-Hydroxyalkyl radical intermediates (RCHOH, R = H, CH3, etc.) are common to the combustion of nearly all oxygenated fuels. Despite their importance in modeling the combustion phenomena of these compounds through detailed kinetic models, the unimolecular decomposition kinetics remains uncertain for even the simplest α-hydroxyalkyl radical, hydroxymethyl (CH2OH). In this study, RRKM/master equation simulations were carried out for CH2OH decomposition to formaldehyde + H between N2 pressures of 0.01-100 atm and temperatures ranging from 1000 to 1800 K. These simulations were guided by methoxy (CH3O) decomposition calculations between pressures of 0.01-100 atm and temperatures ranging from 600 to 1200 K, in both helium and nitrogen. Excellent agreement of the methoxy results was observed for all regions where experimental data exist. Rates were parametrized as a function of both density and temperature within the Troe formalism. Temperature- and pressure-dependent uncertainty estimates are provided, with the largest source of uncertainty being tunneling contributions at very low pressures and at the lowest temperatures. In the regimes relevant to combustion, uncertainties range from factors of 1.4-2 for CH3O decomposition, and from 1.5-2.6 for CH2OH decomposition. The results of this study are expected to have an impact on the high temperature combustion modeling of methanol, as formation rates to CH2O + H from CH2OH are notably different from previous estimates under some conditions.