Use of diabatic and adiabatic representations in three-state close-coupled calculations of He+-He resonant charge exchange collisions

The symmetric resonant charge exchange collision He(1s2)+He+(1s) He+(1s)+He(1s2) has been considered within the laboratory ion energy range 100-3000 eV in a semiclassical three-state close-coupled approximation in the diabatic and adiabatic molecular representations, the latter being obtained by a unitary transformation of the former. The nuclear motion is treated classically using the impact parameter method, while the electronic motion is treated quantum-mechanically. Within the inherent limitations of the diabatic representation chosen, the two sets of calculations yield identical results. The diabatic equations are very nearly decoupled but still show a significant effect of the coupling between the two lowest 2Σsub(g) states of He2+ at low energies. The agreement with experiment is found to be very good. Relative merits and demerits of the use of diabatic and adiabatic representations in atomic collision problems as evidenced by this work are discussed. (author)