| Molecular reaction dynamics, which uses the dynamics of molecular collision to understand the rules of macroscopic chemical reaction, is an important branch of chemical dynamics. At present, ones have been able to carry out the exact full-dimensional quantum dynamic calculation for the four-atomic system. But what chemistry and biology mostly concerns is the large reaction system containing more than four atoms. In resent years, the six-atomic reaction systems have attracted more researchers'attention.Chlorine atom chemistry is of great importance in the atmosphere over a wide temperature range. At low temperature (200-300K) range, Cl atom plays an active role as ozone destroyer. At high temperature (1000-2500K) range, it is important for halogen-hydrocarbon combustion. As a prototypical abio-organic reaction for combustion, the Cl+CH4→HCl+CH3 reaction has been widely studied in recent years. This is because that the reaction can eliminate chlorine atoms from the atmosphere by converting them into inactive HCl. So the reaction has been a hot topic in the molecular reaction dynamics at present.Firstly, in the theoretical dynamic study, the degrees of freedom are quite more for the atom-polyatomic reaction system, which make the ab initio calculations more difficult. Secondly, the quantum dynamic calculations still need reduced-dimensional model due to the limitation of the computer'ability at present. In this work, we developed a full-dimensional analytical potential energy surface (PES) for Cl+CH4→HCl+CH3 reaction, which took the formula of the semiempirical functions and was calibrated based on the new ab initio data at the CCSD(T)/aug-cc-pvtz level. Then, on this PES we carried out the time-dependent wave package dynamics study using semirigid vibrational rotation target model. The main content of this thesis can be summarized as follows:(1) Employing CCSD(T) method and aug-cc-pvtz basis sets in Molpro2006 program packages, we calculated the geometries and frequencies of saddle point, reactant and product for Cl+CH4 reaction. The reaction coordinate path was also optimized. Based on these ab initio data, a semiempirical PES was calibrated. In this process, the geometries and vibrational frequencies of the reactants, the products and the saddle point were adjusted, and the experimental rate constants are also emphasized. Then discussions were involved concerning some characters of the present PES. To test this PES, the reaction kinetic calculations were carried out by using canonical variational transition state theory and canonical unified statistical theory. The comparison with experiments exhibited the present PES could well display both static and dynamical properties of the Cl+CH4→HCl+CH3 reaction(2) A four dimensional quantum dynamics study was reported on the new developed potential energy surface for Cl+CH4→HCl+CH3 reaction. We employed time-dependent wave package method to propagate wave function and semirigid vibrational rotation target model to reduce the system dimensions. Initial state-specific reaction probabilities were calculated and compared with the results of hydrogen absorption reactions O+CH4 and F+CH4. The ground state rate constants were given and in agreement with the experimental measures. The effects of reactant rovibrational excitation were investigated. Sterically dynamical effects of the reactants were also revealed.(3) By using the same method, a time-dependent wave packet dynamic study for the isotope effects of the Cl+CH4/CD4 reactions was conducted. The initial state-specific probabilities exhibited the replacement of hydrogen by deuterium significantly decreased the reaction ability, and the rovibrational excitations of the methane molecule favored the progress of the reaction. Additionally, the ground state rate constants were reported.The important and valuable results in this dissertation can be summarized as follows:(1) The ab initio calculation level of the reaction system was improved and some defects existed in the previous potential energy surface of the system were corrected. A modified global PES was constructed.(2) On the system, the time-dependent quantum dynamic calculations were conducted and provide the reasonable results including the reaction probability, the total scattering cross section and the rate constant, which were in well agreement with the related experimental data. This work has carried out a beneficial trial for the theoretical and experimental research of the Cl+CH4→HCl+CH3 reaction.
|
PDF Full Text Request