The methyl radical combination rate constant as determined by kinetic spectroscopy

The rate constant for the reaction\documentclass{article}\pagestyle{empty}\begin{document}$$ {\rm CH}_{\rm 3} + {\rm CH}_{\rm 3} + {\rm M}\mathop {\longrightarrow}\limits^{k_1 } {\rm C}_{\rm 2} {\rm H}_{\rm 6} + {\rm M} \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\left( {{\rm M = He}} \right) $$\end{document}has been determined by means of vacuum ultraviolet flash photolysis and time‐resolved kinetic spectroscopic observations of the 1504‐Å absorption band of CH 3 . The measurements made using three different sources of methyl radicals (azomethane, dimethylmercury, and ketene‐hydrogen) were in accord and yielded a value for the rate constant of k 1 = (9.53 ± 1.17) × 10 −11 cc molec −1 sec −1 . A detailed error analysis is presented. The f ‐value for the 1504‐Å band of CH 3 is determined to be (2.5 ± 0.7) × 10 −2 .