L3-subshell alignment of argon following charge-changing collisions with protons

Abstract

The alignment of the L3 subshell of Ar induced by electron capture has been studied experimentally for proton impact in the energy range 0.3-1.0 MeV. The experiment is based on the measurement of the angular distribution of the L-MM Auger electrons detected in coincidence with the outgoing neutral H atoms. The results have been compared with the predictions of the Oppenheimer-Brinkmann-Kramers approximation, the strong potential Born approximation, the continuum distorted wave theory and the impulse approximation. The tendency of the measured data towards large negative alignment at high collision energies is in accordance with the asymptotical behaviour characteristic of the capture theories. At lower energies large deviations have been found between the experiment and the theories which can only be partly explained by experimental effects. This finding indicates the failure to understand the capture-induced alignment by the existing theories.