Classical trajectory Monte Carlo calculation of the recoil-ion momentum distribution for positron-impact ionization collisions

Abstract

We investigate ionization processes induced by positron impact on H2 by studying the momentum distributions of the receding ion. To this end, we employ classical trajectory Monte Carlo techniques. The investigation of the recoil ion momentum distribution allows us to shed new light on some known phenomena like the familiar ‘electron capture to the continuum’ peak of electron momentum spectroscopy, and also to unveil new structures which—up to our knowledge—have never been reported in the literature. We propose that some of these new effects represent fingerprints of a strong orientation of low-energy electrons into the direction of motion of the electron–positron centre of mass. We analyse the mechanisms that might give rise to these effects, and relate them to structures in the electron and positron momentum distributions. We also discuss how these theoretical predictions can be put to test in actual positron reaction microscopic experiments.