Theoretical Studies For Dynamics Of Polyatomic Reactions

Focusing on the theoretical dynamics study of atom-polyatomic reaction systems, we have carried out research projects described as following:First, we have employed the SVRT model on the time-dependent wavepacket quantum dynamical calculation on H+HOD and H+CH₄ reactions. The SVRT calculation from a pseudo-vibrationally excited state can be used to investigate the effect of vibrational excitation of the reactant if the pseudo-vibrational state closely represents the actual vibrational state of the reactant being studied. Additionally, such conclusions can be drawn from the calculations from isotopic substituted H+CH4 reaction: 1) In general, the H-atom abstraction is preferred over that for D-atom abstraction in these reactions. 2) The tunneling effect dominates reaction dynamics at low temperature and low collision energy region.Second a chemical accurate global potential energy surface of F+CH₄→HF+CH₃ reaction is constructed with the name ZYH PES, calculations of rate constants are also preformed based on it. The calculations shows the distribution of available energy into HF stretching mode leads to a strongly vibrational excitation through a sudden bond-forming mechanism, meanwhile the out of plane vibration excitation of CH3 moiety is favored due to a gradual bond-forming mechanism. In the outcome of quantum dynamical calculation, resonance structure can be observed from the reaction probability at 2.04 Kcal/mol, which is attributed to the quantum effect. The rate constants obtained from ZYH PES and ab initio calculations using VTST theory are consistent with SVRT calculations, meanwhile the VTST rate constants from MZYH PES can represent experimental data.Third, the comparison of performance of different numerical integrators in the QCT simulation shows the sixth and eighth order routine can excellently keep conservation of total energy in 10"5Kcal/mol, meanwhile, the sixth order routine is the fastest one among them.