Theoretical Studies Of Dynamics For Three Typical Reactions

Molecular reaction dynamics is a science of studying microcopic feature and mechanism of chemical reaction in molecular and atomic level. With the development of theory and experiment, great achievements have been made in this area and have gotten to a new stage which is state-to-state chemical dynamics. 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 scalar properties together with the vector properties, can the fullest picture of the scattering dynamics be obtained. In the thesis, theoretical study of dynamics for several typical reactions including reactions D++H2, H++D2, H'+HBr and Br+HD, especially the stereodynamics, have been investigated by the qusicalssical trajectory method.The calculated results indicate that the reactions D++H2 and H++D2 are prototypical ion-molecular reactions. The H3+system features the presence of a deep well in the ground potential energy surface. Thus the long-time complex is formed in the process of reaction, which leads to a extremely backwark-forward angular distributions and a weak product rotational alignment effect. The increasing collision energy weakens the angular distributions in backwark-forward directions and enhances the effect on the product rotational alignment. For the abstraction reaction H'+HBr, we observed the indirect reactions at high collision energy with backward angular distributions which did not obey the "kinematically constrained", while these indirect reactions are absence at low collision energy. And these indirect trajactories are scarce, most rection trajactories still follow the minimum energy reaction path. The angular distributions are mainly governed by the direct reactions that do follow the minimum energy path, at both low and high collision energies. While the effect on the product rotational aglignment and orientation is sensitive to the indirect reactions. The abstraction reaction Br+HD does not obey the "kinematically constrained", and most rection trajactories violate the minimum energy reaction path. The violation degree from the minimum energy reaction path increases with the increasing collision energy. Therefor, the reaction is not controlded by the traditional abstraction mechanism at the high collision energy. The characteristics of the potential energy surface in the region far away from the collinear geometry have a large influence on the title reaction dynamics. The calculations for reactions systems D++H2, H++D2 and H'+HBr show that the isotope effect plays an important role in the dynamical stereochemistry. And the position of the substituted atom is different, the similar isotopic substituent results in contrary behaviour. The effect of the mass factor on the product rotational alignment varies with the reaction isotopically substituted location at attacking atom or reagent molecule. An increase of mass factor for the reaction H++H2(D2) almost has no significant influence on the alignment of j', while an increase of attacking ion mass enhances the anisotropic distribution of j'. Therefore, the effect of mass factor on the product rotational alignment is sensitive to the mass of the attacking ion, but not sensitive to the mass of the isotopically substituted diatomic. But for H'+HBr abstraction reaction system, an increase of hydrogen mass in reaget molecule weakens the product rotational alignment; while an increase of attacking atom mass enhances the product rotational alignment.