Total Charge-Transfer Cross Sections forHe+andAr+on K, Rb, and Cs: Near-Resonant Reactions Leading to Excited Final States

Total charge-transfer cross sections have been measured for ${\mathrm{He}}^{+}$ and ${\mathrm{Ar}}^{+}$ ions on K, Rb, and Cs atoms, using a crossed-beam arrangement. Ion-beam energies ranged from 10 to 1500 eV. The cross sections were all very large (≳50 ${\mathrm{\AA }}^2$) for asymmetric reactions and give evidence of the anticipated importance of capture into excited states in near-resonant reactions. Predictions (for excited-state products) of a simple two-state theory provide qualitative agreement.