Cross sections forK-shell excitation in slow-ion-atom collisions

Abstract

Absolute cross sections for $K$-shell excitation in projectile ions and target gas atoms are derived from measurements of Auger-electron production in various heavy-ion-atom collisions. Atomic numbers ${Z}_{H}$ and ${Z}_{L}$ for, respectively, the heavier and lighter collision partner were chosen between 5 and 10 with $\ensuremath{\Delta}Z={Z}_{H}\ensuremath{-}{Z}_{L}$ ranging from 0 to 4. The projectile energy was varied from 40 to 600 keV. The cross sections are compared with previous theoretical data. In general, good agreement is found between theory and experiment at the low-energy limit. At higher energies, increasing deviations are observed due to the increasing vacancy occupation of the $2p\ensuremath{\pi}$-molecular orbital. For most collision systems, $K$-vacancy sharing ratios are derived in excellent accord with theoretical results in the whole energy range. However, for light-collision systems (${Z}_{H}+{Z}_{L}\ensuremath{\le}13$), absolute cross sections as well as the sharing ratios are found to be inconsistent with the previous theories. Possible reasons for these inconsistencies are given. The effect of the multiple ionization on the $K$-sharing ratios of the collisions partners is discussed.