Charge-Transfer Collisions Involving Electron Transfer to Excited States

A crossed-beam technique was used to measure total nonresonant charge-transfer cross sections of the following reactions over an energy range from about 0.5 to 20 keV: ${\mathrm{Li}}^{+}$ + Cs→ Li + ${\mathrm{Cs}}^{+}$, ${\mathrm{Li}}^{+}$ + Rb→ Li + ${\mathrm{Rb}}^{+}$, ${\mathrm{Li}}^{+}$ + K → Li + ${\mathrm{K}}^{+}$, ${\mathrm{Hg}}^{+}$ + Cs→ Hg + ${\mathrm{Cs}}^{+}$. For each reaction, the minimum energy defect occurs for transfer to an excited state. The cross sections show typical nonresonant characteristics with the measured maxima corresponding to these energy defects. The production of photons resulting from deexcitation of the Li ($2p$) state formed by charge-transfer collisions was also measured over the same energy range for the reactions involving Li. These photon cross sections (with larger experimental uncertainties than the total cross sections) were "normalized" to the total cross section in the near-adiabatic region using semiempirical relationships. Transfer to an excited state is the dominant channel in the near-adiabatic region with transfer to the ground state becoming increasingly important with increasing impact velocity. The discussion of the ${\mathrm{Hg}}^{+}$ + Cs results includes statistical weight considerations.