Atmospheric pressure absolute rate coefficients have been determined for the gas phase reaction of OH radicals with methyl chloride ( k l ) , methylene chloride (k2), and chloroform (k3) over an extended temperature range using a laser photolysisDaser-induced fluorescence technique. The rate coefficients are best described by the following modified Arrhenius equations: kl(295-955 K) = (4.64 ? 0.58) X 10-12(T/300)0.89exp{(-1447 t 75)/T} cm3 molec-I s-I. k2(295-955 K ) = (2.01 '-+ 0.17) X 10-12(T/300)1.wexp{(-771 ? 48)/T} cm3 molec-' s-'.
k3(295--774 K ) = (2.71 t 0.23) X 10-13(T/300)1.52exp{(-261 ? 42)/T} cm3 molec-' s-I.
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-2 were found to measurably increase (up to a factor of 2) the rate coefficients for k3 between 400-775 K, with the effect increasing with increasing temperature. A similar, yet much smaller (ca. 20-35%) increase was observed for k2 between 675-955 K. No effect was observed for kl at 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 of k p and k3 on photolysis intensity at elevated temperatures. The puzzling and disconcerting discrepancy between previously published high temperature measurements of k3 and transition state model predictions is reconciled with these latest measurements.