Theoretical Study Of The Stereo-dynamics Of The Reactions Of H + HeH~+

As a new frontier branch in the field of molecular reaction dynamics, stereochemistry dynamics has attracted a lot of interest and is becoming a hot area. In the recent decades, the reaction of He+H₂⁺ has received considerable attention for its importance in the studies of ion-molecule reaction dynamics. In order to understand the dynamics of the HeH₂⁺ system fully, in this work, we study the reverse reaction H + HeH⁺. Theoretical study of the stereo-dynamics of the reaction H + HeH⁺ has been performed with quasi-classical trajectory (QCT) method on a new ab initio potential energy surface constructed by Ramachandran et al in 2009.This dissertation is composed of four chapters. The outline of the molecular reaction dynamics, stereochemistry dynamics and potential energy surface (PES) of reaction systems are presented in the first chapter. In chapter two, the vector correlations and the related theories of QCT are introduced. In chapter three, the stereo-dynamics of the reaction H + HeH⁺ is extensively studied. Chapter three is composed of four sections. In the first section, we give a brief introduction of the status and significance of the research. In section two, we study the stereo-dynamics of the reaction H + HeH⁺(v = 0, j = 0)→H₂⁺ + He at different collision energies. The results indicate that the rotational polarization of product H₂⁺ presents different characteristics for different collision energies. The rotational angular momentum vectors j′of the product is not only aligned, but also oriented, and a preference of changing from the"in-plane"reaction mechanism to the"out-of-plane"mechanism emerges. The product H₂⁺ is mainly forward scattering, and with the increase of the collision energy, the tendency of forward scattering increases rapidly. Although we have observed indirect reaction mechanism at the lower collision energy of 0.1eV, it has little influence on the reaction. The reaction is mainly dominated by the direct reaction mechanism. The tendency of the rotational alignment parameter ? P2 (j′?k)? of the product indicates that the title reaction belongs to"light–light–light"(LLL) mass combination and the corresponding PES is attractive, which implies that the exoergic process of the reaction takes place on the entrance valley of the PES. In section three, we study the effect of reagent rotational excitation on the stereo-dynamics of the H + HeH⁺→H₂⁺ + He reaction. The results indicate the reagent's rotational excitation has a considerable influence on the distribution of k-j′correlation and the k-k′-j′correlation. The rotational polarization of product H₂⁺ presents different characteristics for different rotational excitation. The PDDCSs are also found to be sensitive to the reagent's rotational excitation. In section four, at the collision energy of 1.50 eV, we study the isotopic effect on the stereo-dynamics of the reaction H + HeH⁺. First, we freeze the mass of the target molecule and observe the influence caused by the mass change of the attack atom on the stereo-dynamics of the reaction and then we freeze the mass of the attack atom to observe the influence of the target molecule's mass. The results indicate the mass variation of the target molecular has more influence on the product rotational angular momentum than that of the attack atom. The product rotational angular momentum j′is not only aligned, but also oriented along the positive direction of the y-axis and the degree of the orientation is affected strongly by the mass of the target molecule. Moreover, whether the attack atom or the target molecular is replaced by the corresponding isotope, the value of ? P2 (j′?k)?can not change regularly with the increase of the mass factor. We think it may be caused by the influence of the long-range interaction. In addition, the DCS of the reaction is very sensitive to the mass variation of the attack atom and the target molecule, which reflects the apparent isotope effect. Finally, a brief summary and prospect of this paper are given in chapter four.