Electron emission in collisions of 0.5 MeV/u C²⁺₂ai

A new multi-spectrometer apparatus has been built and tested. It can be used to simultaneously measure the energy and angular distribution of electrons ejected between 0° and 8° with respect to the beam direction and to detect the recoil ions produced in ion-atom collisions. The multispectrometer apparatus consists of a 30° parallel plate electrostatic analyzer with a large position sensitive detector (PSD), a recoil ion time of flight (RITOF) spectrometer, and a charge state analyzer.

This work focuses on measuring the energy and angular distribution of electrons ejected between 0° and 8° with respect to the beam direction in coincidence with the recoil ion charge state and the exit charge state of the projectile ions in ionizing collisions between 0.5 MeV/u C²⁺ projectile and H₂ target. Electrons with kinetic energy between 0 eV and 1450 eV have been detected. Doubly differential cross sections have been obtained from the data. A prominent feature in the electron energy distribution is the binary encounter peak. The experimental binary encounter electron production cross sections are compared with theoretical results obtained using the impulse approximations.

Cusp electrons are nearly exclusively produced in collisions which involve single ionization of both projectile and target. Binary encounter electrons, on the other hand, are produced in collisions in which the projectile remains intact and does not change charge. The only electrons which are ionized in the collisions are the binary encounter electrons themselves.