Measurements on post-collision interaction in L-shell ionisation of Ar by electron impact at large excess energies

Abstract

The authors have measured the energy shift epsilon of the L₃M₁M₂₃ (³P₂) Auger line (Auger energy E_A approximately=191 eV, level width Gamma (ArL₃)=130 meV) at large excess energies in the energy region from E₁=100 eV up to E₁=10 keV with an experimental error of only +or-5 meV. This high precision was achieved using as reference line a neighbouring satellite line with a value of Gamma an order of magnitude smaller than Gamma (ArL₃). The authors' experimental results are in full agreement with previous experiments on the post-collision interaction (PCI) shift epsilon in Ar L-shell ionisation but, due to the accuracy of the new data, their experiment reveals for the first time a precise functional dependence of the PCI shift epsilon on the excess energy E₁ at large excess energies for electron impact ionisation. They observe that epsilon (E₁) changes abruptly at E₁ approximately=1 keV and remains constant for larger excess energies. This behaviour is not predicted by published theories. Recently, however, Sandner (1985) has indicated the existence of such a constant PCI shift at large E₁.