AB Initio Dynamics Study On The Reaction BR+DMSO

In this thesis, the direct dynamics methods have been use to study the microcosmic mechanism and rate constants of the reactions: Br+CH₃SOCH₃ products.By means of Gaussian03 program, the geometries and frequencies of the stationary points (reactant, hydrogen bond complex, transition state, and products) are calculated at the BH&HLYP/6-311G(2d,2p) level. The minimum energy path (MEP) is calculated at the same level by intrinsic reaction coordinate (IRC) theory. Furthermore, with the selected points along the MEP. In order to gain more accurate energy profile, the energies of the selected points on the MEP are refined at MC-QCISD level. Finally, the canonical variational transition state theory with small-curvature tunneling correction are applied to obtain the reaction rate constants by using POLYRATE-Version 9.1 program.For the reactions mentioned above, the potential surface information is obtained, including geometries, energies, gradients, and force constants matrices of the stationary points (reactants, transition states and products), some extra points along the minimum energy path (MEP), the reaction enthalpies(â–³^H₂₉₈0) and potential barriers(â–³E) with zero-point energy correction(ZPE). Subsequently, the rate constants of the above-mentioned reactions are calculated using the variational transition state theory (VTST). The theoretical results obtained are in good agreement with the experimental values. It indicates that the present calculations can provide reliable prediction of the rate constants for the above-mentioned reactions at higher temperatures.The reaction Br + CH₃SOCH₃ has two alternative reaction pathways, i. e., the HBr and CH₃ forming channels. From the calculation the branching ratios of the temperature dependence, it can be seen that two reaction channels is competitive reaction. The rate constant for the reaction channel to yield HBr is the major channel. The reaction channel to yield CH₃ is minor channel over the whole temperature region 200—2000 K. Both the variational effect and the tunneling effect are small over the whole temperature region.