H/D + Li2 LiH/LiD + Li reactions studied by quantum time-dependent wave packet approach

Abstract

The isotopic effect is a significant way to further understand the reaction mechanism without greatly changing the system. However, the isotopic effect of the H + Li2 reaction has received little attention in previous theoretical studies. Furthermore, as a deep potential well exists on the reaction path, obtaining convergent result is very time-consuming. So some approximate methods were used in previous theoretical calculations. However the Coriolis coupling effect plays an important role in the reaction, and thus whether these approximate methods are reasonable needs further testing. Based on the potential energy surface (PES) reported by Song et al., the dynamical calculations of H/D + Li2 LiH/LiD + Li reactions are carried out by time dependent quantum wave packet method with second order split operator in a collision energy range from 0 to 0.4 eV. In order to obtain the convergent results, lots of convergence tests are carried out and because the Coriolis coupling effect plays an important role in the reaction, all the number of projections of total angular momentum J are included in the present calculation. The dynamical properties such as reaction probability, integral cross section, differential cross section are calculated and compared with previous theoretical values. Large discrepancies are found between present results and the values obtained from Gao et al. especially at high collision energies. Owing to the fact that the same PES is applied to the calculation and Gao's results of total angular momentum J=0 accord well with the present values, we suppose that the parameters used in the calculation have little influence on the final results and the main discrepancies are attributed to the number of projections of total angular momentum which are cut off in Gao et al.'s calculation. In order to verify our speculation, the numbers of projections of total angular momentum which are 1, 5, 10, 15, 20, and 25, are considered in the calculation, respectively. The results indicate that the main discrepancy between present values and the results obtained from Gao et al. can be attributed to the number of projections of total angular momentum used in Gao et al.'s calculation that is not convergent, and that the present values are more accurate than previous theoretical studies for all the numbers of projections of total angular momentum which are included in the calculation. Furthermore, when the H atom is substituted by the heavy isotope D atom, the reaction probability and integral cross section become large. However, it does not generate large effect on the reaction mechanism. The forward and backward symmetry differential cross section signals indicate that the complex forming reaction mechanism dominates the reaction.