Electron-impact double ionization of argon studied by double and triple coincidence techniques: The first (e,3e) experiment

Angular correlations between the three outgoing electrons in the double ionization of argon by electron impact have been measured for the first time. Double and triple coincidence techniques are used to determine simultaneously all final electron energies and angles, and provide fourfold and fivefold differential cross sections, respectively. The angular distributions are consistent with a two-step model for the double ionization mechanism. The present results clearly show the feasibility and potentiality of (e,3e) experiments.