Time-dependent Quantum Wave Packet Simulations Of The K+HF And H+HBr Reactive Scattering

Molecular collision and reaction dynamics is a subject of studying microscopic mechanism of chemical reaction in molecular and atomic level. It can provide basic knowledge for interpreting general phenomena in the chemical reactions, and become the base of the macroscopic reaction dynamics. As one of the most important theoretical methods for molecular collision and reaction dynamics, time-dependent quantum wave packet method has been successfully applied in the gas phase atom-diatom reactive scattering and has played an important role in surface science, inelastic scattering and hydrolyzing investigation. In this paper, detailed dynamics of K+HF and H+HBr systems have been studied using the time-dependent quantum wave packet scattering theory.The calculations for K+HF reaction are carried out on a new ab initio potential energy surface, which is developed by R.Sayós et al. The results indicate that this reaction occurs with threshold energy of about 0.7 eV, and the probabilities rise with the increasing collision energy and reach a plateau region at higher energy. The effects of the initial rovibrational excitation of reagent HF on reaction show that the reaction should be significantly enhanced by vibrational excitation of HF, but not very sensitive to initial rotational excitation. The relative cross sections for both of the ground state and the vibrational excitation of HF are also calculated, and by comparing with QCT results relatively good agreement with experiment was obtained. The calculated absolute cross sections for ground state of HF have identical threshold energy and similar trend with experiment. In addition, the rate constants are calculated and discussed, which increase with the temperature exponentially.The calculations for H+HBr system are also carried out on the latest ab initio potential energy surface, and reaction probabilities and rate constants are all obtained. The calculated reaction probabilities are relatively large in the whole energy range, and have no threshold energy. Very oddly, the obtained rate constants are about two orders of magnitude larger than previously experimental and theoretical results, whereas the previous theoretical results calculated only with collinear reaction configuration of the same PES are in accordance with experiment. In order to find the origin of the disagreement, calculations with limited angleθin reactant Jacobi coordinates are performed again. The obtained probabilities can feedback the reaction feature of this system more accurately. It has threshold energy of about 0.05 eV, and increase slightly with the energy. In addition, the obtained rate constants are much better, and in good agreement with experiment in general. The potential energy surface and dynamics progress are analyzed in detail, and a potential well is found locate on the potential energy surface for abstraction reaction in T-shape geometry. It implied that the large discrepancy between the calculated results and experiment might be due to this potential well.