3 Experimental Kinetics and Thermodynamics Group, Physical and Chemical Properties Division, National Institute of Standards and Technology, Gaithersburg, MD. 20899, USA.

The abstraction of hydrogen atoms by hydroxyl radicals is the determining factor in the tropospheric lifetimes of most saturated organic compounds, including halogenated species containing one or more C-H bonds. This work is part of an ongoing effort at the University of Lille and the Computational Chemistry Group at NIST, to create efficient and reliable computational chemistry tools useful in describing the energetics and mechanisms of halocarbons in the atmosphere.

Our plan has been: (i) to find the minimum level of ab initio molecular orbital theory suitable for predicting the reactivity of a set of halocarbons for which reliable experimental data exist, and (ii) to apply this level of theory to the prediction of the reactivity of new species.

In this talk, we report the results obtained for the reactions of OH radicals with a series of haloalkanes, which serve as a prototype. Especial emphasis will be paid to the choice and validation of efficient theoretical methods that can provide a semi-quantitative description of the kinetics of these processes as a function of temperature.