Anti-capture into the continuum in electron-atom ionization

Abstract

Collisional ionization by electrons and positrons is a major unsolved problem in atomic collisions. Because the projectile can transfer significant momentum to the loosely bound atomic electrons and/or the target core, this cannot be treated as a semi-classical three-body collision between the projectile, the target core and a loosely bound electron, even at 100 times the ionization energy. To elucidate this problem, we are studying single and double binary effects in correlation experiments between outgoing projectile and ejected electrons as a function of projectile energy, and projectile and ejected electron exit angles. We have made, what we believe to be, the first observation of anti-capture to the continuum, the electron equivalent of the Thomas peak in ion-atom scattering. We also have observed a very sharp drop in the double differential cross section at 45°. This is probably due to the fact that two identical particles cannot have the same momentum and energy. In addition, our results show that the probability of scattering one electron to a particular angle or two is given only by the geometry in zero order. Thus, the double differential cross section is much larger than one might expect on the basis of a second Born calculation.