Charge transfer and ionisation in collisions between positive ions

A fast intersecting beam technique has been applied to the study of Li+-Li+ collisions and H+-X+ collisions (where X = Al, Ga, In, Tl and Ba). The 50-600 keV projectile beams of Li+ and protons were made to intersect the corresponding Li+ and X+ target beams, of energy 6-20 keV, at 90o inside an ultra high vacuum chamber. Total cross sections σ(Li2+) for the production of Li2+ ions by the combined processes of charge transfer and ionisation, were measured over the centre of mass energy (Ecm range 53-240 keV using a double beam modulation technique. Similarly total cross sections σ(X2+) have been determined in the Ecm range 50-597 keV. A remeasurement of the cross section σ c for the charge transfer reaction H+ + He+ → H + He2+ was carried out using a coincidence technique in the Ecm range 49-141 keV. The present results for σc are in good agreement with these measured by earlier authors and confirm that values of σc previously measured in this laboratory overestimated the cross section by 25% due to an arithmetical error. Finally, the charge transfer contributions to the total X2+ production cross sections σ(X2+) (where x = Al, Ga, In and Tl) have been determined in the Ecm range 50-249 keV using a coincidence technique. The ionisation contributions to σ(X2+) were determined by the corresponding relations σI σ(X2+ - σC. (author)