Coincidence angular correlations between scattered, ejected and Auger electrons in electron impact double ionization

We present a new, unprecedented electron impact (e,3–1e) study of the ionization of the 2p-inner shell of argon. For the first time, multi-angular distributions are measured for the coincidence detection of two electrons emitted with the same kinetic energy (205 eV) as the Auger electron issued from the electronic rearrangement of the target. The incident energy is chosen such as to leave the third, unobserved electron with either a small or a large kinetic energy, or else with the same energy of 205 eV. In the latter case, the three final state electrons are fully indistinguishable (or at 'resonance'). A rich structure is observed in the angular correlation diagrams. At the highest energy, the observed pattern may qualitatively be explained by considering the Auger emission as a 2-step process. At lower energies, and in particular when all three outgoing electrons have identical energies, the picture dramatically changes, bearing almost no trace anymore of the 2-step process, and being very likely dominated by strong interference and post collisional interaction effects.