Stopping power and the concept of effective ion charge at low energies.

A new formalism for the calculation of the ion-matter interaction phenomenon was developed by incorporating the atomic electron shell structure. This formalism allows for discrimination among the electrons of the target atoms according to their average positions with respect to the shell structure of the projectile ion. By doing so, we are able to show a strong dependence of the ion energy loss on its electron shell distribution. Thus a detailed quantum mechanical description of the moving ion is necessary to predict its precise trajectory and energy loss inside matter. The concept of an "effective charge" in the context of the electron stopping power formalism is emphasized and extended.