He2+ formation in collisions between fast He+ ions

A fast intersecting beam technique similar to that used previously in this laboratory has been used to study He2+ formation in He+-He+ collisions at CM energies within the range 54-229 keV. Absolute total cross sections for He2+ formation have been determined and the separate contributions from charge transfer and ionization have also been obtained. The process of simultaneous electron loss by both He+ ions has been shown to be relatively unlikely even at the highest energies considered. The measurements usefully extend previous lower energy data and, while agreement with these is generally satisfactory, some discrepancies have also been noted. The energy dependence of the measured cross sections for charge transfer indicate an unusually broad structure in general accord with one theoretical prediction. Comparisons with a number of theoretical descriptions have been made for both charge transfer and ionization. (Author)