Ab Initio Study of the Kinetics of the Reactions of Halomethanes with the Hydroxyl Radical. Part 1: CH2Br2

摘要

Ab initio calculations using the Molier-plesser perturbation theory were carried out on the H-atom abstraction reaction from dibromomethane by hydroxyl radical attack. Geometry optimization and vibrational frequency calculations at the MP2 level were performed on all reactants, products and the transition state with both the 6-311G(d,p) and 6-311G(2d,2p) basis sets. Utilizing the geometry parameters optimized at the MP2/6-311G(2d,2p) level of theory, single point energy calculations were carried out with increasing basis set sizes, from 6-311G(2d,2p) to 6-311++G(3d,3p) and with both the MP2 and MP4SDTQ methods. Canonical transition state theory was used to predict the rate constants as function of the temperature (240-380 K). For the kinetic parameters of this reaction, reasonable agreement with the experimental values was obtained at the PMP2/6-311F(3df, 2p)//Mp2/6-311G(2d,2p) level of theory. With the largest basis set, 6-311++G(3df,3pd), the calculated rate constants are in very good agreement with their experimental counterparts.