Theoretical Study Of Free Radical Reactions

Four parts of the work are included in this thesis: The study on the reaction kinetics of OH radical with hexachlorobenzene (HCB); the reaction of Criegee radical; the calculation of the rate constant of the reaction of C2H2 and the supplement and the improvement for the program SIMPLEX. DFT and AM1 methods were used to study the reaction of OH radical with HCB, a poisonous chemical in gas phase, which is considered to be one of the decomposing ways of I-ICB in the atmosphere. The optimized structures of the reactants, the products and the transition states were found. A reasonable reaction path was determined through IRC calculations. The activation energy obtained is in good agreement with the experimental values. The intermediate Criegee radical is the source of some important pollutants in the atmosphere. It is difficult to study the reaction of Criegee radical experimentally since the Criegee radical is very unstable, so we study the reaction in theory on both thermodynamics and dynamics. A potential energy surface (PES) accurate enough can provide all the information needed for a chemical reaction, the curve from a valley (reactant) of the PES to another valley (product) of the PES along the minimum energy path (MEP) form the reaction path. The rate constant of the reaction can be calculated from the MEP using variational transition state theory (VTST). The rate constants of some reactions of C2H2 are calculated using VTST. Some supplement and improvement have been done to the structure optimization program SIMPLEX.