Dominant screening process in the projectile electron loss for F- + Ar collisions

Abstract

A comparison between projectile electron loss cross sections for negative, F − , and positive, He + , projectiles is presented for collisions with Ar target. The behavior of the two collision systems is similar for the projectile electron loss with target ionization. For projectile electron loss without target ionization (the so-called screening electron-loss process), quite different situations are presented for the studied positive and negative projectiles. For He + + Ar, the loss without target ionization collision channel is negligible for intermediate-to-low energies. On the other hand, for F − + Ar, this collision channel is the dominant one in the total projectile electron loss at intermediate-to-low velocities. The roles played by coupling with the electron capture by the projectile collision channel and by the very different binding energies for negative and positive projectiles are discussed.

Free-collision model calculations for the electron detachment of anions by noble gases

“…Sant'Anna et al have shown that the first-order direct effect of the target electrons on the detachment of the projectile electrons (the antiscreening mode [7,8]) and the Table 1. Configurations, electron affinities (EA) (eV) [13,14] and average kinetic energies (KE) (eV) [15,16] second-order direct loss-ionization channel can be considered negligible for these projectiles at the velocities considered here [9,10]. Q m and Q 0 have been calculated using rootmean-square velocities of the active electrons, u rms , which are obtained from the average kinetic energies of the anion and the neutral atom, respectively.…”

“…The results are compared with experimental data for the absolute total and partial (the latter only for C − ) electron detachment cross sections of anions colliding with noble gases from [2,5]. These data lie in a velocity region where the main mechanism for the electron-loss cross sections is due to the interaction between the active projectile electron(s) and the screened Coulomb field of the target nucleus, the so-called screening mode [6,7], since the direct effect of the target electrons on the detachment of the projectile electrons (the antiscreening mode [7,8]), together with the direct loss-ionization channel, can be considered negligible [9,10]. The total cross sections were calculated considering only the single-and double-electronloss channels; the multi-electron character of the projectiles has been taken into account within the independent particle model (IPM).…”