The reactions of methyl radicals with atomic and molecular oxygen

The reaction of methyl radicals with atomic and molecular oxygen was studied with a photoionization mass spectrometer. The methyl radicals were generated by reacting oxygen atoms with ethylene in a fast‐flow tube reactor. The rate constant for the reaction of methyl radicals with oxygen atoms was (1.0 ± 0.2) × 10 −10 cm 3 /molec · sec with no significant variation with temperature over the range of 259–341°K. The reaction of methyl radicals with molecular oxygen involves both a two‐body reaction, having a rate constant {article}{empty}{document}array*20c k_ 3a = (10- 12.54 ± 0.35)exp [(- 940 ± 250)T- 1] & cm³ / molec · sec array{document} and a three‐body recombination having a negative temperature dependence. The methyl peroxy radical could be observed at its steady‐state concentration. The rate constants determined at low pressures are compatible with the values determined at higher pressures by flash photolysis. Formaldehyde appears to be a major product of the two‐body reaction of CH 3 with O 2 , and also of the reaction of CH 3 O 2 with oxygen atoms.