Saturation of Penning Ionization at Small Distances Probed by Coincidence Techniques

Abstract

Penning ionization can be the major inelastic process in gas-phase collisions of fast metastable-excited atom beams, yet elastic scattering generally obscures detailed examination of this process. Using a coincidence technique, we have now extracted double-differential cross sections for the ionization processes. Our first results for the ${\mathrm{He}}^{*}\left(2^{3}S\right)+\mathrm{Ar}$ interaction give fresh insight into this often-studied system, most notably by revealing saturation of the absorptive (Penning) channel at distances slightly smaller than are accessible in thermal-energy experiments.