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 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−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.

Electron loss from fast heavy ions: Target-scaling dependence

“…Electron-loss cross sections have been measured for atomic targets ranging from helium to xenon [5][6][7][8][9][10][11][12][13][14]. These studies have shown that for lighter targets, typically meaning for Z T < 10, where Z T is the target nuclear charge, the cross sections increase rapidly, e.g., approximately as Z n T , where n ∼ 1.4-1.7.…”

“…More recently, Santos et al [7,26] further explored these concepts and used C 3+ and He + data to determine the ratio σ anti /σ e , which combined with the impulse approximation, enabled them to estimate the average number of active target electrons for the antiscreening mode. This was done as a function of collision energy and fitted to…”

“…They found that even though the binding energies of the ionized electrons are quite different for the two projectiles, the antiscreening and screening processes have the same relative magnitudes and energy dependences. Several studies by Montenegro and co-workers [6,7,[28][29][30] also used the PWBA to calculate electron loss from few-electron ions such as He + , C 3+ , and O 5+ . Of particular relevance to the present work is that these studies implied that the scaling for the screening channel is influenced by saturation effects occurring for heavy targets, i.e., for large Z T [29,31],.…”

Electron-recoil ion and recoil ion-projectile coincidence techniques applied to obtain absolute partial collision cross sections

“…Despite the fact that the multiple ionization of rare gas targets in collision with ions has been extensively investigated over the past several decades, 1 it still continues to pose experimental [2][3][4][5][6][7][8][9][10][11][12][13][14][15] and theoretical challenges. 13,[16][17][18][19][20] For example, studies focused on the comparison between bare or partially stripped ions shed light on the role of the projectile effective charge state in direct multiple ionization processes of rare noble gases.…”

“…3,8,9,15,21 We illustrate the method presenting measurements of ionization of helium atom, resulting from collisions with C 3 + ions. In order to check the accuracy of our method, we compare our results to the works of Santos and co-workers, 2 where a time of flight spectrometer inside a gas cell target was used to study the collision between C 3 + and rare gas atoms. We also extend their measurements from 3.5 MeV to 5 MeV.…”