The Ab Initio And Dynamics Study Of ArH₂ ⁺ System

Atom-molecule ion reactions are of fundamental importance as they play an important role in plasmas physics,astrophysics and high energy physics. As an important atom-molecule ion reaction, as well as the reaction between rare gas and the ion of the hydrogen gas, the reaction Ar+H₂⁺ deserves further investigation, but to our surprise, few study can be reached. Accurate potential energy surface is the foundation of dynamical calculation. The reaction probability and cross-section of chemical reaction can be calculated based on potential energy surface. The principal work of this article is that, we have constructed a new ab initio potential energy surface of the reaction Ar+H₂⁺ and studied the stereochemistry of the reaction based on the new potential energy surface (PES).In the first chapter of this paper, we have given the outline of the molecular reaction dynamics and dynamics stereochemistry as well as the PES of reaction systems. In chapter two, the vector correlation and related theories of quasi-classical trajectory (QCT) are given in a brief introduction. The main work of this paper is listed in the third and the fourth chapter, and in the third chapter, the procedures of constructing a three-dimensional potential energy surface were described in detail. We constructed the ab initio potential energy surfaces for Ar+H₂⁺ reaction at the level of aug-cc-pV5Z based on the many-body expansion method. We have calculated the cross-sections for Ar+H₂⁺(v=0-2, j=0)→ArH++H on this new surface at E col=1eV, 3eV, 6eV. The vibrational energy dependence of the cross section is pronounced: a weakly increase from v =0 to v =1; a very slow decrease for large v .The results were compared with the transition state theory (TSH) results reported by Sally Chapman, which demonstrates that the agreement is basically well although there are slight differences. That is to say, our new global PES for the reaction Ar+H₂⁺ is reasonable. In addition, to obtain a clear understanding of the reaction mechanism, the variation of inter-nuclear distances of H-H+, Ar-H+, and Ar-H is presented as a function of propagation time. It shows that the Ar atom collides with the HH+ molecule and forms an ArH+ that moves away immediately. This process is consistent with the direct reactive dynamics mechanism. It also shows that with the increase of the energy, the occurrence of the reaction is obviously advanced, which means it is the collision energy that works much more, rather than the vibrational excitation.To study some of the nature of the Ar+H₂⁺ reaction further, in the fourth chapter, the stereodynamics of the Ar+H₂⁺ and its isotopic substituted reactions have been performed by QCT based on our new PES. The vector correlation between products and reagents for the chemical reaction Ar+H₂⁺ has been studied at different mass factors. The results indicate that the rotational polarization of product ArH+ presents different characters for different mass factors. The product rotational angular momentum j′is not only aligned, but also oriented along the direction perpendicular to the scattering plane. With the increase of the mass factors, the orientation of the product rotational angular momentum j′becomes weaker. We have also studied the effect of the vibrational and rotational energies. The results show that both the collision energy and the rotational produced obvious effect on the stereodynamics of the reactions of Ar+H₂⁺. Finally, a brief summary and prospect of this paper are given in chapter five.