Electron transfer to Ar2+from rare-gas atoms

Measurements of the sigma 21 cross section for Ar 2+ ions in helium and xenon have been made between 60 and 200 keV. The level crossing theory was found to give cross sections which were much smaller than the experimental values in all the rare-gas targets except helium. An improved version of the Rapp-Francis non-crossing theory (1962) gives reasonable predictions for both heavy and light rare-gas targets and this is probably the dominant electron transfer process at these energies.