A modified laser photolysis/laser-induced fluorescence technique has been used to measure atmospheric pressure absolute rate coefficients for the reaction of hydroxyl (OH) radicals with the chlorinated methanes (CH,CI, CH2C12, and CHCI,). Data have been obtained for these compounds over the widest temperature range (292-800 K) that has been reported in the literature using a single experimental apparatus. The temperature dependence of the rate data is best represented by the following threeparameter expressions: CH,CI: 8.38 2 1.07 x T'3"='"'"1 exp [ -2387.4 Uncertainties in the pre-exponential and exponential term are expressed as 95% confidence intervals. For the temperature exponent, error limits represent a ?lo% change in the total error of best fit. The degree of curvature in the Arrhenius plots appeared to increase with increasing C1 substitution of the reactant, However, the uncertainty in the temperature exponent for the CH,Cl data was large in comparison with the other chlorinated methanes. Thus, data of greater precision a t elevated temperatures are necessary to further explore this relationship. The rate coefficients were compared with recent semiempirical and transition state theory models for haloalkane-OH hydrogen transfer reactions over a temperature range of 250-800 K. The transition state model of Cohen and Benson was in excellent agreement with the CH&1 and CH,CI, data. The semiempirical structure activity relationship developed by Atkinson represented the best fit of the * This article has been reviewed by the Risk Reduction Engineering Laboratory, US.Environmental Protection Agency, Cincinnati, Ohio and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of EPA, nor does mention of trade names or commercial products constitute endorsement or recommendation for use.'