Ionization of helium by proton and H₂⁺ impact studied by projectile and recoil ion momentum spectroscopy

“Projectile momentum spectroscopy and cold target recoil ion momentum spectroscopy (COLTRIMS) have been applied to study single ionization of He by proton and H2+ impact. In the case of the H2+ projectiles a kinematically complete experiment on single ionization was performed by measuring the fully momentum analyzed projectiles and recoil ions in coincidence. The electron momentum was deduced from momentum conservation. From the projectile momentum measurement, doubly differential single ionization cross sections as a function of the longitudinal and transverse projectile momentum were obtained. For the case of H2+ + He collisions, clear signatures of the post-collision interaction between the outgoing projectiles and the electrons were observed in the momentum spectra of all collision products simultaneously. The importance of the post-collision interaction between the projectile and the ionized electron was demonstrated by the studies"--Abstract, page iv.