Direct Combined ab Initio/Transition State Theory Study of the Kinetics of the Abstraction Reactions of Halogenated Methanes with Hydrogen Atoms

摘要

Theoretical calculations were carried out on the H-,C1-,and F-atom abstraction reactions from a series of seven substituted halogenated methanes(CH_3C1,CH_2Cl_2,CHC1_3,CC1_4,CHF_3,CHF_2C1,and CHFCl_2)by H atom attacks.Geometry optimizations and vibrational frequency calculations were performed using unrestricted M011er-Plesset second-order perturbation theory(UMP2)with the 6-311++G(d,p)basis set.Single-point energy calculations were performed with the highly correlated ab initio coupled cluster method in the space of single,double and triple(pertubatively)electron excitations CCSD(T)using the 6-31 l++G(3df,3pd)basis set.Canonical transition-state theory with a simple tunneling correction was used to predict the rate constants as a function of temperature(700-2500 K),and three-parameter Arrhenius expressions were obtained by fitting to the computed rate constants for elementary channels and overall reaction.