Electron emission from binary collisions with ZProjectile ≤ ZTarget

Abstract We have measured doubly differential cross sections for electron emission in ion-atom collisions. In one set of experiments, 0.5 MeV/u He 2+ projectiles impinged on the target atoms He, Ne, Ar, Kr and Xe and molecules N 2 and O 2 ; in another set, H + (energy ranging from 2.0 to 6.0 MeV) and 0.75 MeV/u N q + ( q = 2–7) collided with Ar targets. In both cases, emitted electrons were observed under 0°. Major interest was directed upon the position of the Binary Encounter Peak, which is commonly assumed to follow a simple kinematic model. Surprisingly the peak is significantly shifted towards lower energies. For comparison we calculated spectra with the Plane Wave Born Approximation and the Plane Wave Approximation. These do not show in general good agreement with our experimental data, presenting large discrepancies not only in absolute values but also in the behaviour with the target atomic number.