Ab Initio Calculations for Kinetic Modeling of Halocarbons

The thermochemistry and reaction kinetics of halogenated hydrocarbons have been investigated by ab initio methods in order to improve our understanding of their flame chemistry and likely roles in flame suppression. Bond additivity corrections at the G2, G2(MP2), CBS-4 and CBS-Q levels of theory were developed for fluorinated and chlorinated C 1 and C 2 species, including saturated and unsaturated compounds. The resulting enthalpies of formation are in excellent agreement with experimental values. Transition states for the reactions of H atoms with hydrofluoromethanes were characterized at up to the G2 level of theory, and application of transition state theory yielded rate constants in good accord with experimental results. A similar analysis for H and OH reactions with CH 3 I also agrees with the known thermochemistry and kinetics. These investigations provide insight into the major product channels and the temperature dependence of the rate constants. The implications for flame suppression by haloalkanes are discussed.