Temperature Dependence of the Rate Constant and Product Distribution of the Reaction of CH3 Radicals with O(3P) Atoms

The kinetics and product distribution for the reaction of methyl radicals, CH3, with ground-state, O(3P) oxygen atoms, have been investigated at temperatures up to 925 K and at constant bath gas (He) concentrations of about 3.2 × 1016 cm-3. With a photoionization/time-of-flight mass spectrometer (TOFMS) as an analytical tool, precursor species, reactants, and products were observed simultaneously. The radicals were produced by an excimer laser pulse (λ = 193 nm), in the cophotolysis of acetone, CH3C(O)CH3 and sulfur dioxide, SO2. In addition to the dominant product, formaldehyde (CH2O), carbon monoxide (CO) was detected as the only other main product. The yields for both products were found to be independent of temperature with values of ΦCH3+O(CH2O) = 0.84 ± 0.12 (2σ) and ΦCH3+O(CO) = 0.15 ± 0.06 (2σ). However, the overall rate constant for this reaction shows a slight increase with temperature with kCH3+O = (2.4 ± 0.3) × 10-10 exp(-(202 ± 60) K/T) cm3 molecule-1 s-1 between T = 354 and 925 K at [He] = 3...