Observation of electron-electron scattering in electron capture by fast protons from He

Abstract

The angular distribution of electrons ejected from He with about the projectile velocity in coincidence with the capture of the other electron by the projectile in 1-MeV proton-He collisions has been measured. The signature of the proton-electron-electron scattering leading to transfer ionization has been observed for the first time as a peak at about 90\ifmmode^\circ\else\textdegree\fi{} in the angular distribution of the ejected electrons. The effect is in qualitative agreement with theoretical predictions.