Saturation Effects in Charge-changing Collisions with Multiply-charged C and O Ions

Abstract

The electron loss of multiply-charged dressed ions by heavy neutral atoms can have a significant contribution from collisions with small impact parameters. This can render one of the two competing mechanisms which govern the electron loss, i.e. the screening, highly non-perturbative. The other mechanism (antiscreening) is due to electron-electron interactions and its contribution can be treated perturbatively. The dependence of the total electron loss cross sections on the target atomic number, Z2, presents a strong saturation as the value of Z2 increases. Calculations based on the Plane Wave Born Approximation present such a behavior for the antiscreening but not for the screening, since this saturation is related to a non-perturbative regime. In this work we compare data for the total electron loss cross sections of C3+ and O5+ ions by H, He, Ne, Ar, Kr and Xe targets, with energies ranging from 1.0 to 3.5 MeV, with calculations for the screening contribution based on the free-collision model. This comparison shows that, for highly-charged ions, the electron capture and direct target ionization channels play a major role in the description of experimental electron loss data.