The Ab Initio And Dynamics Study Of Triatomic Reaction System

Being typical and very simple ion-molecule reactions, He⁺H₂⁺ and H-⁺H₂ are considered to be the prototype systems to test the quality of the new theories and experiments. And the extensive studies can help us to study the other complex ion-molecule reactions. Besides, the two reactions and their isotopic reactions are of interest in understanding the collision processes in interstellar media, the plasma, and high-energy physic studies.This dissertation is composed of two parts. The first part is the constructions of potential energy surfaces (PESs) for He⁺H₂⁺ and H-⁺H₂ reactions based on ab initio theory. The reaction cross-sections have been calculated using the quasi-classical trajectory (QCT) method. In the second part, the stereodynamics of the He⁺H₂⁺ and its isotopically substituted reactions have been performed by QCT.Accurate PES is the foundation of dynamical calculation. The reaction probability and cross-section of chemical reaction can be calculated based on PES. Due to the importance of the PES, the ab initio potential energy surfaces for He⁺H₂⁺ and H-⁺H₂ reactions at the level of aug-cc-pV5Z are derived. The total integral cross-sections as a function of collision energy at v=0-3 have been calculated based on the He⁺H₂⁺ PES. We find that the vibrational energy is much more effective than translational energy to promote this reaction. The cross sections enlarge obviously with the increasing of the vibrational quantum number. In the v=0 case, the present measurements are somewhat lower than the previous theoretical and experimental data. In the v=1-2 cross-sections, the present results are slightly higher than previous results near threshold. For the v=3 initial vibrational state, the presents results agree nicely with the experimental cross sections, especially below collision energy ET=0.7eV. The total integral cross-sections as a function of collision energy at v=0 have also been calculated for the H-⁺D2 and D-⁺H₂ reactions based on H-⁺H₂ PES. The results are consistent with the previous time-dependent wave-packet results.In order to understand the dynamics of an elementary reaction fully, it is important to study not only its scalar properties, but also its vector properties. Vector properties, such as velocities and angular momentum, possess not only magnitudes that can be directly related to translational and rotational energies, but also to well-defined directions. Only by understanding both above properties can the fullest picture of the scattering dynamics be obtained. In this paper, the stereodynamics of the He⁺H₂⁺ and its isotopically substituted reactions have been performed by QCT based on Palmieri et al. The vector correlation between products and reagents for the chemical reaction He⁺H₂⁺ has been studied at different collision energies. The results indicate that the rotational polarization of product HeH⁺ presents different characters for different collision energies. The product rotational angular momentum j′is not only aligned, but also oriented along the direction perpendicular to the scattering plane. The product HeH⁺ tends to be scattered forward as the collision energy decreases. The vector correlations for the chemical reactions He⁺H₂⁺/HD⁺ have been calculated. And a pronounced isotopic effect is also revealed. Some interesting results are found in the calculations.