Effect of Long-Range Forces in Near-Resonant Charge Transfer: Application toHe++ K, Rb, and Cs

Near-resonant charge transfer in asymmetric collisions is often dominated by long-range forces due to polarization and sometimes to ion-quadrupole interactions. These interactions can lead to regions of strong coupling at large distances. The parameters necessary for estimating the cross sections by a modified Demkov formula (for strong coupling without crossing) can be obtained from a knowledge of simple atomic properties such as ionization potentials and polarizabilities. These formulas are applied to the calculation of the cross sections for the ${\mathrm{He}}^{+}$ + K, Rb, and Cs asymmetric charge-transfer reactions and are compared with the experimental measurements of Peterson and Lorents. For these systems several inelastic channels are open and the theory predicts the relative abundances of the various excited states of He (n=2).