A quantitative study of alkyl radical reactions by kinetic spectroscopy. II. Combination of the methyl radical with the oxygen molecule

The kinetics of the reaction\documentclass{article}\pagestyle{empty}\begin{document}$${\rm CH}_{\rm 3} + {\rm O}_{\rm 2} (+ {\rm M}) \to {\rm CH}_{\rm 3} {\rm O}_{\rm 2} {\rm (+ M)}$$\end{document} have been studied, using the technique of flash photolysis and kinetic spectroscopy to follow the methyl radical concentration. The order of the reaction lies between 2 and 3 throughout the range of pressure from 25 to 380 torr at 22°C, and the results are consistent with a single reaction sequence:\documentclass{article}\pagestyle{empty}\begin{document}$$\begin{array}{l} {\rm CH}_{\rm 3} + {\rm O}_{\rm 2} \mathop {{\rm \rightleftharpoons}}\limits_{\rm b}^{\rm a} {\rm CH}_{\rm 3} {\rm O}_{\rm 2} ^* \\ {\rm CH}_{\rm 3} {\rm O}_{\rm 2} ^* {\rm } + {\rm M}\mathop {{\rm \rightarrow}}\limits^{\rm c} {\rm CH}_{\rm 3} {\rm O}_{\rm 2} {\rm + M} \\ \\\end{array}$$\end{document} The limiting values of the third‐order rate coefficients at low pressures are (3.6±0.3) × 10 11 1. 2 mole −2 sec −1 when M is neopentane, and (0.94 ± 0.03) × 10 11 1. 2 mole −2 sec −1 when M is nitrogen. The limiting value of the second‐order rate coefficient at high pressures is (3.1 ± 0.3) × 10 8 1. mole −1 sec −1 . The rate constant for the independent second‐order reaction\documentclass{article}\pagestyle{empty}\begin{document}$${\rm CH}_{\rm 3} + {\rm O}_{\rm 2} \to {\rm CH}_{\rm 2} {\rm O} \to {\rm OH}$$\end{document} is shown to be not much greater than 2 × 10 5 1. mole −1 sec −1 , so that this reaction does not complete significantly with the combination reaction. This new interpretation is contrary to currently accepted views.