Theoretical Investigations On The Reactions Mechanisms And Kinetics Of Alkyl Halide And Alkyl Hydrogen With Several Radicals

Using ab initio and density function theory (DFT) chemistry methods, we studied CH₃OOH, CH₃CH₂OOH,CH₃Cl with active radicals and atoms reactions. Furthermore, based on the potential energy surface (PES) obtained, kinetics properties for series reactions of haloalkane and hydrofluoroethers. Theoretical prediction of the rate constants, the temperature dependence of branching ratios are provided for further studying and using these reactions experimentally. The important and valuable results in this thesis are summarized as follows:1. Theoretical studies on the mechanisms of CH₃OOH/ CH₃CH₂OOH + OH reactions. The mechanisms and kinetics studies of the OH radical with alkyl hydroperoxides CH₃OOH and CH₃CH₂OOH reactions have been carried out theoretically. The geometries and frequencies of all the stationary points are calculated at the UBHandHLYP/6-311G(d,p) level, and the energy profiles are further refined by interpolated single-point energies (ISPE) method at the MC-QCISD level of theory. For two reactions, five H-abstraction channels are found and five products (CH₃OO, CH₂OOH, CH₃CH₂OO, CH₂CH₂OOH and CH₃CHOOH) are produced during the above processes. The rate constants for the CH₃OOH/CH₃CH₂OOH + OH reactions are corrected by canonical variational transition-state theory (CVT) within 250–1500 K, and the small-curvature tunneling is included. The total rate constants are evaluated from the sum of the individual rate constants and the branching ratios are in good agreement with the experimental datas.2. Theoretical studies on the mechanisms of CH₃Cl + Cl reactions. The theoretical study on the H-abstraction reaction mechanism and variational rate constant of the reaction CH₃Cl + Cl are investigated at MP2 and CCSD(T) levels with 6-311++G** basis set. The rate constants for the H-abstraction reaction of CH₃Cl + Cl are calculated by the classical transition state theory and canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) correction in the temperature range 220-2000K. The results are consistant with experiment.