Calculations of ion-atom interactions relating to resonant charge-transfer collisions

The interaction between an atom and ion of the same element leads to gerade and ungerade states of the diatomic molecular ion. The energy splittings between the gerade and ungerade states determine the cross section for resonant charge transfer. Using the JWKB approach these energy splittings are derived from the asymptotic forms of the wave functions for the isolated atom and ion. Pseudopotential calculations of the splittings are reported for ${\mathrm{Li}}_2^{+}$, ${\mathrm{Na}}_2^{+}$, ${\mathrm{Rb}}_2^{+}$, and ${\mathrm{Cs}}_2^{+}$, and are used together with previous ab initio and model-potential calculations to test the JWKB method. The comparison shows that the method is sufficiently reliable to facilitate accurate calculations of the cross sections for resonant charge transfer at low energies.