Quantum Time-dependent Wave Packet Study On The Reactive Scattering F+HBr And Br+H₂

The time-dependent quantum wave packet method is one of the most attractive approaches for study the atom-molecular collisions and understanding the reaction dynamics. It has been widely used in atom-diatom, diatom-diatom and ion-diatom reactions and many meaningful results have been obtained. In this thesis, the time-dependent quantum wave packet method was used to study the reactive scattering F+HBr and Br+H2, respectively.The latest LEPS potential energy surface constructed by Persky et al was used in the calculations for F+HBr. The reaction probabilities increased dramatically near the zero collision energy and then decreased slightly with further increasing collision energy, which were corresponding well to the behavior of a barrier-less reaction. The effects of the reagent HBr excitation were also examined, it was found that both the vibrational and rotational excitation of reagent HBr have negative effects on the reactivity of the F + HBr. The effects of vibrational excitation were stronger at low collision energy whereas the influences of rotational excitation were stronger at high collision energy. The obtained integral cross section decreased quickly at low collision energy and then became flat, which reflected the general feature of such exothermic reactions. The calculated rate constant was much closer to the experimental results than that of the quasi-classical trajectory calculations, but the former was a bit larger than latter, indicating that the quantum effects played an important role in the reaction F+HBr.Time-dependent quantum wave packet calculations were also carried out for Br + H2 on a new global ab initio and a semi-empirical extended LEPS potential energy surface. It was shown that on ab initio surface the reaction threshold energy was much lower, the reaction probabilities, cross sections and rate constants were much larger than on extended LEPS surface. The possible reasons and mechanism for the dynamical difference on the two potential energy surfaces were analyzed and discussed combining with the feature of them. The effects of the initial ro-vibrational excitation were also studied and the results indicated that on both of the potential energy surfaces the reactivity of Br+H2 was strongly enhanced by the vibrational excitation of the reagent molecular H2 whereas the enhancement by the rotational excitation was not so remarkable. Comparison of rate constants with experimental measurement and the previous calculations showed that the ab initio surface is more suitable for quantum dynamic calculation than extended LEPS one.