PCI effects in (e,e' Auger) and (e,2e) cross sections: Ar 2p

Abstract
Ionisation of the argon 2p core level by high-energy electrons and the relaxation process via Auger emission were investigated by electron-electron experiments. At energy losses exceeding threshold by a few eV both the energy spectrum and the angular distribution of the Auger electrons measured in coincidence with scattered electrons of fixed energy and momentum transfer show post-collision interaction (PCI). The results preclude an interpretation of the scattered-Auger-electron angular correlation in terms of a pure alignment effect and constitute a detailed test of the ionisation mechanism near inner-shell threshold. The authors show that, even at low momentum transfer, the measured angular distribution of both the scattered and Auger electron pair (e,e' Auger) and scattered and ejected electron pair (e,2e) show relevant deviations from the predictions of first-order collision theories.