Triple-differential cross-section measurements of electron-impact ionization of argon 3s in the backward scattering direction

The triple-differential cross section for the electron-impact ionization of the 3s orbital of argon has been measured over the complete backward scattering direction of the ejected electron, using a magnetic angle changer in a conventional (e,2e) spectrometer. The results reveal the position and relative magnitude of the recoil scattering peak in the cross section for this target, and enable a detailed comparison with recently published calculations of argon 3s ionization which have been performed using a hybrid distorted-wave Born approximation—R-matrix approach. These theoretical calculations show dramatically improved agreement with the experimental results, in comparison with earlier approaches, but puzzling discrepancies still remain