Reaction of methyl radicals with O(3P), O2 and NO

Abstract

The reactions of methyl radicals with atomic and molecular oxygen and nitric oxide were studied using a photoionization mass spectrometer. The methyl radicals were generated by the reaction of oxygen atoms with ethylene in a fast-flow reactor. In the measurement of the rate constant for the reaction of methyl radicals with oxygen atoms, the approach of the methyl radicals to their steady state concentration was measured for initial concentrations of ethylene of 0.1–1 mTorr. With less than 0.2 mTorr of ethylene, a rate constant of (1.38±0.46)×10−10 cm3 molecule−1 sec−1 was obtained. The rate constant for the reaction of methyl radicals with molecular oxygen was measured by two methods; Stern–Volmer plots and the steady-state approach method. Both results showed the existence of intercepts when the measured effective rate was extrapolated to zero pressure. The observed ratio of rates of the CH3+O2 to the CH3+O reaction was in agreement with the previous measurement by Washida and Bayes. The reaction of methyl radicals with nitric oxide showed no evidence of a two body process. The three body rate constant of this reaction was (2.4±0.8)×10−30 cm6 molecule−2 sec−1 with M=He.