Formation of Free Electrons in Collisions of Xe Atoms with α Particles

Abstract

We have measured the cross sections of elementary processes occurring during collisions of impinging ³He²⁺ particles with kinetic energies in the range 1–100 keV with Xe atoms, which are accompanied with the formation of free electrons and ions in different final charge states: Xeⁿ⁺ (n = 1–6) and He^{(2 – m)+} (m = 0–2). We distinguish between ionization processes, in which the impinging α particle does not change the charge state, and processes of capture of one or two electrons, which lead to the formation of a singly charged helium ion or atom with additional removal of electrons from the xenon atom to the continuum. We have determined the cross sections of formation of free electrons in each of these processes and calculated the contribution of multielectron processes to the formation of free electrons. It is shown that upon a change in the energy of collisions between ³He²⁺ ions from 1 to 100 keV (the velocity of an impinging ion changes from 0.12 to 1.2 a.u.), the mechanism of removal of electrons from the xenon atom changes basically. For low approach velocities of particles, the formation of an autoionization state of the quasi-molecule and its subsequent decay take place. At higher velocities (V > 0.7 a.u.), free electrons are mainly formed because of an abrupt change in the potential energy of electrons when a fast α particle approached the nucleus of the xenon atom.