Isotopic effects in low-energy lithium-hydrogen collisions

Abstract

The cross sections and rate coefficients for the inelastic processes of mutual neutralization, ion-pair formation, and (de)-excitation in lithium-hydrogen collisions are calculated based on the ab initio electronic structure [J. Phys. B: At. Mol. Opt. Phys. 32, 81 (1999)] and the hopping probability current method [Phys. Rev. A 88, 052704 (2013)] for the nonadiabatic nuclear dynamics. For each given set of collisional parameters, calculations of the probability current evolution were repeated $2.621\phantom{\rule{0.16em}{0ex}}44\ifmmode\times\else\texttimes\fi{}{10}^{9}$ times, and this leads to a high accuracy of the inelastic state-to-state transition probabilities, the cross sections, and finally, the rate coefficients. The isotopic effects on the processes in collisions $^{6}\mathrm{Li}/^{7}\mathrm{Li}+\mathrm{H}/\mathrm{D}/\mathrm{T}$, where (H/D/T) represents hydrogen, deuterium, and tritium, for different isotopes are studied. In addition, the deexcitation resonance processes $^{6,7}\mathrm{Li}(2p\ensuremath{\rightarrow}2s)+\mathrm{H}/\mathrm{D}/\mathrm{T}$ were treated by the branching probability current method. It is found that the isotopic effects are different for different collisional partners and for different electronic states involved into a process, varying from negligible effects for high-lying Li states to strong effects for low-lying Li states. The resonance transition process is one with the strongest isotopic effects: replacing H by T changes the rate coefficient by up to four orders of magnitude. Unfortunately, there is no experimental data for the processes with strong isotropic effects, only for the processes with moderate effects, up to 60%.