AbstractAtmospheric pressure absolute rate coefficients have been determined for the gas phase reaction of OH radicals with methyl chloride (k1), methylene chloride (k2), and chloroform (k3) over an extended temperature range using a laser photolysis/laser‐induced fluorescence technique. The rate coefficients are best described by the following modified Arrhenius equations:\documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 (295 - 995) = (4.64 \pm 0.58) \times 10^{ - 12} ({\rm T/300)}^{{\rm 0}{\rm .89}} \exp \{ (- 1447 \pm 75)/T\} cm^3 molec^{ - 1} s^{ - 1} $$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 (295 - 995) = (2.01 \pm 0.17) \times 10^{ - 12} ({\rm T/300)}^{{\rm 1}{\rm .09}} \exp \{ (- 771 \pm 48)/T\} cm^3 molec^{ - 1} s^{ - 1} $$\end{document}\documentclass{article}\pagestyle{empty}\begin{document}$$ k_1 (295 - 774) = (2.71 \pm 0.23) \times 10^{ - 13} ({\rm T/300)}^{{\rm 1}{\rm .52}} \exp \{ (- 261 \pm 42)/T\} cm^3 molec^{ - 1} s^{ - 1} $$\end{document}Measurements were obtained as a function of excimer photolysis intensity and are compared with previous results and extended to higher temperatures. Photolysis intensities in excess of 12 mJ‐cm−2were found to measurably increase (up to a factor of 2) the rate coefficients fork3between 400–775 K, with the effect increasing with increasing temperature. A similar, yet much smaller (ca. 20–35%) increase was observed fork2between 675–955 K. No effect was observed fork1at any temperature. Relative absorption coefficient measurements at 193.3 nm indicated that chlorinated methane photolysis increases with both increasing temperature and increasing chlorine substitution. These measurements suggest that reactant photolysis may be responsible for the observed dependence ofk2andk3on photolysis intensity at elevated temperatures. The puzzling and disconcerting discrepancy between previously published high temperature measurements ofk3and transition state model predictions is reconciled with these latest measurements. © 1993 John Wil