Transfer ionisation in slow collisions of multiply-charged ions with atoms

Abstract

Systematic experiments on transfer ionisation processes Aq++B to A(q-k)++Bi+(i-k)e+ Delta E have been performed where A and B are rare-gas atoms, q is the charge state of the incident ions (up to 7 for Ne, 9 for Ar, 12 for Kr and 15 for Xe), k is the number of captured electrons found with the projectile long after the collision (k=1, 2 or 3) and i is the charge state of the slow recoil ion (measured by a time-of-flight coincidence technique). The projectile energies range from 3q keV to 15q keV; however, with very few exceptions, the charge-state fractions Fi of recoil ions were found to be independent of the energy in the energy range studied. The ionisation of five additional target electrons in 7% of the two-electron-capture collisions of Xe15+ ions with Xe atoms shows the importance of transfer ionisation in such collisions. The observed charge-state fractions of the recoil ions strongly depend on k, the number of electrons captured, and on q, the charge state of the projectile; the mean charge state (i)= Sigma jjFj/ Sigma jFj increases strongly with increasing k and q. In general, the investigated processes are exoergic, and the charge states of the recoil ions produced are correlated with the potential energy available in the collision system. When the charge-state fractions Fi observed for a given target atom are plotted as a function of the maximum potential energy Delta E calculated for transitions between ground states they fall on common curves which are only specified by the charge state i and the number of electrons k captured indicating that Fi depend explicitly neither upon the projectile species nor upon the incident charge state.