Absolute cross sections for electron loss, electron capture, and multiple ionization in collisions ofC3+with noble gases

Abstract

Absolute charge-state-correlated cross sections for projectile electron loss, electron capture, and target multiple ionization in collisions between ${\mathrm{C}}^{3+}$ ions and noble gases have been measured for energies between $1.3$ and $3.5$ MeV. The data have been compared with other similar absolute cross sections existent in the literature for several projectiles. Calculations for the single-loss$\ensuremath{-}$multiple-ionization channel have been performed for the screening mode, using both an extended version of the classical-impulse free-collision model and the plane-wave Born approximation (PWBA), and for the antiscreening mode within the PWBA. The energy dependence of the average number of target active electrons which contribute to the antiscreening has been described by means of a simple function, which is ``universal'' for noble gases but, in principle, projectile dependent. A method has been developed to obtain the number of active target electrons for each subshell in the high-velocity regime, which presented physically reasonable results. Analyses of the dependences of the single-capture and transfer-ionization (SC and TI, respectively) processes on the projectile charge states showed that, for He, equally charged bare and dressed projectiles have very similar cross sections; the latter thus acting as structureless point charges. A behavior similar to that in the SC has been observed for the pure single ionization of He by projectiles with different charge states and of the other noble gases by singly charged projectiles. It has been shown that the ${q}^{2}$ dependence of the pure-single and total-ionization cross sections, predicted by first-order models, is only valid for high-collision velocities. For slower collisions, the electron capture process becomes more relevant and competes with the ionization channel, a feature which grows in importance as the projectile charge state increases.