Theoretical Investigation On Reaction Mechanism Of Ployatomic System Using Direct Dynamics Methods

Great achievements of direct dynamics have been made recently with innovation of computer technology and development of the methods, which make it possible to study reaction mechanism of polyatomic system by putting insight in dynamics process. The method has achieved considerable results and will be more and more popular. The VASP code within the frame of the density function has been used for dynamics study of three system: CH₂O+CH₃, BCl₃+H, F₂+C₂H₄. Our results provide detailed information on the reaction mechanism of the three system. The studies not only are very helpful for understanding the reaction mechanisms deeply but also show the characters of the direct dynamics. The first is an one channel reaction and this is the first study by dynamics. It is still a formidable challenge to study such a reaction in the gas phase by traditional dynamics because of the large number of freedom degrees for the system. There are two reaction channels for the second system. For the H abstraction channel, we obtain the results well agree with that of the ab initio calculation. For the Cl elimination channel, we found the transition state and the intermediate led by the sample trajectory of the dynamics. The reaction mechanisms of the third system is long-time puzzled and the reaction features are changed in solvent or in cryogenic matrix. Our studies supported the Miller's radical mechanism. We have also extended the discussion to the mechanism of the reaction in polar solvents and cryogenic matrix, and deduced in principle the uniform mechanism as in the vapor phase.