Differential measurements on ion-atom collisions in the energy range 500-3000 eV. IV. H+-noble gas atom collisions

Abstract

For pt. III see abstr. A33295 of 1970. H+-rare gas atom collisions (He, Ne, Ar, Kr, Xe) have been studied in the energy range 0.5<or=E0(Lab)<or=3 keV and in the angular range 0.5<or= theta <or=10 deg. Differential cross sections have been measured for the main collision processes: elastic collision, charge exchange, simple excitation of the atom, excitation of the atom to autoionizing levels. In most of the cases, the elastic cross sections are in rather good agreement with theoretical semi-classical-or semi-quantal-cross sections calculated from ab initio potentials. As the atomic number of the target atom is increased, the charge exchange probability becomes larger, while it shows a stronger angular dependence. These features are explained by considering the energy diagrams of the molecular systems, in which the 'exchanged' state potential curves become closer to the ground state curve as heavier atoms are taken. The excitation process evolves in the same way as the charge exchange, but its threshold in tau is slightly larger. As no excited state (dissociating into H+ plus the excited atom) interacts with the ground state, the excitation is considered as a two step process, taking place via the charge exchange. The excitation of the target atom to autoionizing levels is qualitatively explained, in the MO model framework, by the promotion of two p electrons, and can be considered also as occurring via the charge exchange.