An ab initio study of the kinetics of the reactions of halomethanes with the hydroxyl radical. 1. CH2Br2

Ab initio calculations were carried out with Moller-Plesset second- and fou rth-order perturbation theory (MP2 and MP4), and the coupled cluster method , CCSD(T), on the H atom abstraction reaction from dibromomethane by hydrox yl radical attack. Geometry optimization and vibrational frequency calculat ions at the MP2 level were performed on reactants, products, and the transi tion state using the 6-311G(d,p) and 6-311G(2d,2p) basis sets. The geometry parameters optimized at: the MP2/6-311G(2d,2p) level of theory were used i n single-point energy calculations with increasing basis set sizes, from 6- 311G(2d,2p) to 6-311++G-(3df,3pd) at both the MP2 and MP4(SDTQ) levels of t heory. Canonical transition-state theory was used to predict the rate const ants as a function of the temperature (250-400 K). It was found that the ki netic parameters obtained in this work with the spin-projected method PMP4( SDTQ)/6-311++G(3df,3pd)//MP2/6-311G(2d,-2p) are in reasonable agreement wit h the experimental values. The prospect of using relatively low level ab in itio electronic structure calculations aimed at the implementation of inexp ensive semiquantitative "screening tools" that could aid scientists in pred icting the kinetics of similar processes is also discussed.