Theoretical Studies Of Stereodynamics For Several Typical Reactions

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 together above properties can the fullest picture of the scattering dynamics be obtained. In the thesis, the dynamical stereochemistry of three typical reaction systems including H + H2, Cl + H2 and S + D2 reactions have been studied by using the quasiclassical trajectory theory and time-independent quantum reactive scattering theory. At the same time, studies on the dynamics of the N+OH reaction has been performed via time-dependent quantum reactive scattering theory.Calculations indicate that the product rotational alignment effect for the S + D2 reaction is weak. The reason is that there is a deep well on the potential energy surface (PES) of the S + D2 reaction. BW2 PES of the Cl + H2 reaction has long-range van der Waals minima in both the entrance and exit channels, but the product rotational alignment effect obtain on the BW2 PES is stronger than that on the G3 PES. This surprising phenomenon probably implies that the product rotationalalignment is mainly controlled by the properties in the transition state area on the PES. The calculations for H + H2 and Cl + H2 reaction systems 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.Accurate three-dimensional time-dependent quantum wave packet calculations for N + OH reaction show for the first time that the initial state-selected reaction probabilities are dominated by resonance structures, and the lifetimes of the resonance are quantitatively in subpicoseconds. The N + OH reaction system has no energy barrier in the entrance channel on the PES; instead, there are double wells along the reaction path, which leads to that the integral reaction cross sections are not strongly dependent on either translational energy or initial rotational and vibrational state.