A QUASI-CLASSICAL TRAJECTORY STUDY OF MODE-SPECIFIC REACTION DYNAMICS IN THE C1+HOD AND H+HOD REACTIONS

We present the results of extensive quasiclassical trajectory studies of the reaction Cl + HOD --> OH + DCl, OD + HCl and its counterpart with Cl replaced by H, based on the H3O potential surface of Schatz and Elgersma. Emphasis in this study has been given to studying the effect of vibrational excitation of the reagents on the branching between the OH and OD product channels. The specific initial vibrational states considered are (000), (100), (001), and (004), and we consider initial translational energies up to 2.7 eV. In the quasiclassical calculations, the initial vibrational states are defined using good actions which have been calculated using a Fourier series expansion method. We demonstrate that the initial states defined this way are close to being stationary for each vibrational mode.The resulting reactive cross sections for the Cl and H atom reactions are comparable in magnitude, with the Cl cross sections being systematically higher than the H cross sections. For both reagent atoms, branching to the OH product is enhanced when the (100) initial state is considered, and branching to OD is enhanced when the initial state is (001). Branching to OD is very strongly enhanced if the initial state is (004). The branching ratio is similar in magnitude for Cl and H atom reactions, though the energy dependence is different. No evidence is found that the Cl causes enhanced collision induced scrambling of the HOD vibrational excitation while the reagents approach. Product state distributions for both reactions are also presented at selected energies and compared with experiment and with previous calculations. Effects of zero point violation are studied, and it is found that requiring each product diatomic to have zero point energy leads to unphysically small cross sections and inaccurate cross section ratios. However, constraining just the zero point energy of the newly formed diatomic leads to accurate ratios and realistic cross sections.