Influence of the electron binding energy in the distortion of the initial state in ion-atom collisions

In this work, we propose a modified continuum distorted wave (CDW) theory for ion-atom ionization that incorporates an electron effective-mass model for the bound electron-projectile distortion in the entrance channel. Distorted wave theories have been shown to be adequate when the projectile impact energy is high enough but, as the projectile velocity decreases, both CDW and continuum distorted wave--eikonal initial state (CDW-EIS) approximations exhibit remarkable discrepancies when compared with the available experimental data, in particular for highly charged ion impact. Our modified CDW approximation incorporates the active electron binding energy in the distorted wave description of the initial state. We found very good agreement with experimental data in a single ionization doubly differential cross section for multiply charged projectiles and impact energies as low as 50 keV∕amu.