Proton-impact excitation of lithium using a time-dependent close-coupling method

Abstract

A time-dependent close-coupling method, formulated within the framework of a rotational function expansion in two-dimensional cylindrical coordinates, is used to investigate excitation processes in proton-lithium collisions. As a first check, the calculated $\text{Li}(1{s}^{2}2s)\ensuremath{\rightarrow}\text{Li}(1{s}^{2}2p)$ excitation cross sections are compared and shown to be in reasonable agreement with the previous Cartesian lattice time-dependent Schr\"odinger equation results for collision energies at 5, 10, and 15 keV. As a result, additional calculations are carried out to determine the cross sections not only for the $\text{Li}(1{s}^{2}2s)\ensuremath{\rightarrow}\text{Li}(1{s}^{2}2p)$ transitions, but also for the Li($1{s}^{2}3l$) transitions for a wider range of proton-impact energies from 2 to 50 keV. Reasonable agreement is found when further comparison of the dominant Li($1{s}^{2}2p$) excitation cross sections is made with data obtained from crossed-beams experiments and other close-coupling methods. With the present extensive and large-scale calculations, the convergence for the reported results is also addressed, especially for the less-dominant Li($1{s}^{2}3l$) transitions, with respect to the box sizes, number of coupled channels, and propagation time.