Theoretical study of near-resonant charge-exchange collisions of H⁺ with alkali atoms

Our earlier study of the H⁺-Cs collision is extended to the lighter H⁺-alkali-atom systems. The previous one-electron projected-valence-bond approximation is further simplified and improved by the use of an effective screened Coulomb potential to represent the alkali⁺ core. This method is found to reproduce very accurately the results of a complete all-electron calculation performed on the (Li-H)⁺ system. Total cross sections for charge exchange into H(n=2)+alkali⁺ are obtained from diabatic 7-state close-coupling calculations. The theoretical results nicely agree with the available experimental data for the H⁺-K and -Rb systems. On the other hand, the calculated cross section for H⁺-Na is significantly smaller than the experimental results; possible sources of this discrepancy are discussed.