Application Of SVRT Model To Reaction Of H+CD₄â†'HD+CD₃

Molecular reaction dynamics is a branch of chemical reaction dynamics. It is an important topic of molecular reaction dynamics to study the chemical reaction with the method of the quantum theories. At present, rigorous quantum dynamics calculations are limited only to systems involving not more than four atoms. For the further development, one will carry out quantitatively accurate quantum dynamic study for the systems including more than four atoms. But with decreasing of atomic number, the quantity of calculation will go up tremendously. In order to solve that. recently, the Semirigid Vibrating Rotor Target (SVRT) model has been proposed as a general theoretical model for practical dynamic polyatomic molecules. Reliable quantum dynamics calculation can be carried out for the system of more than four atoms using the SVRT method. Now the SVRT model is applied to study the reaction of H+CD4→HD+CD3 in four mathematical dimensions.In the SVRT model, the target molecule is treated as a simirigid rotor composed of two rigid parts. The two rigid parts can exercise only one dimensional relative motion along the coordinate connecting the center-of-mass of the two parts. Their spatial motion is considered as a general asymmetric rotor. Practically, the SVRT model for the atom-polyatom reaction is a natural generalization of the exact atom-diatom reaction. So the quantity of calculation is reduced effectively. This model can be applied to the polyatomic molecule in that there is a weakly bond, and after the reaction the molecule can be split into two parts. In the study, the model permits realistic quantum dynamics calculation for a general atom-polyatom reaction with just four mathematical dimensions. Using the SVRT model, excellent quantum results have been obtained for the H+H2O, H+D2O and H+CH4 reactions.In this paper, the SVRT model is applied to study the reaction of H+CD4→HD+CD3. In the reaction, the target molecule is treated as two parts of D and CD3, and the whole system is described with four dimensions. Our dynamic calculation is carried out on a recent ab initio potential energy surface (PES) of Jordan and Gilbert. The TDWP method also is employed as a computational tool. Reaction probability, cross section and rate constant are calculated for the title reaction from the ground state (v=0, j=0, m=0) and from the four rotational excited states (v=0, j=1,m=0), (v=0, j=1, m=1), (v=0, j=2, m=0)and (v=0, j=2, m=1) of the molecule CD4.Numerical results including reaction probability, cross section and rate constant are discussed in this article. By analysis and comparison of the results, we draw the conclusion as follows: Firstly, the quantum tunneling effect is quite pronounced. Second, the reaction probability shows resonance-like oscillatory structures in its dependence on collision energy. Thirdly, the probability goes up obviously with the rising of the rotational quantum number j. This indicates that the ascension of the rotational excited state is propitious of the split of the C-D bond in the molecule CD4. This feature plays a very important role in the field of the bond-selected chemist. Fourthly, the resonance structure disappears in the energy dependence of integral cross-section due to the summation of partial waves. At the same translational energy, the cross-section increases with the rising of the rotational quantum number j, and declines with the rising of the quantum number m. In the last, we find that the reaction rate constant and the cross-section have the similar rule for the quantum numbers j and m.Finally, at present our calculated results are one of the most accurate results of the reaction H+CD4→HD+CD3. And it also shows some microscope dynamics mechanism of the system. The present results also demonstrate that the SVRT model for atom-polyatom reaction provides a practical and accurate approach for studying chemical reactions involving polyatomic molecule.