CHEMICAL-KINETICS OF METHYL OXIDATION BY MOLECULAR-OXYGEN

Four fuel-lean mixtures of methane and oxygen diluted in argon were st udied behind reflected shock waves at temperatures from 1550 to 2200 K . The reaction progress was determined in situ by state-selective lase r absorption of OH radicals and CO molecules. The rate coefficients of the CH3 + Oz reactions were determined via detailed computer modeling with the GRT-Mech 1.2 reaction mechanism and theoretical calculations using the RRKM master equation formalism. The derived rate coefficien t expressions, in units of cm(3) mel(-1) s,(-1) are 2.87 x 10(13)e(-15 340/T) for the reaction CH3 + O-2 --> CH3O + O and 1.85 x 10(12)e(-102 24/T) for the reaction CH3 + O-2 --> CH2O + OH. The experimental rate coefficient of the CH3O + O channel was found to be in good agreement with the canonical variational transition state theory. The potential energy barriers relative to CH3 + O-2 were found to be 15.4 kcal/mol f or the CH2O + OH channel and 0.9 kcal/mol for the entrance barrier, th e latter indicating a tight transition state. The derived reaction mod el for the high-temperature oxidation of methyl by molecular oxygen is shown to be self-consistent, in harmony with theory, and in agreement with essentially all experimental data available on this reaction sys tem.