Cross sections for (multiple) ionization of ions in collisions with electrons

Recently we proposed a new semiempirical analytical parametrization for the shape of ionization cross sections resulting from collisions of ions with various projectiles [1]. It was shown that the incorporation of the correct threshold behaviour as given by the Wannier theory is the crucial point to obtain good agreement with experimental results from threshold to high ene rgies and leads to a unified view of collision processes in very different systems. While the shape of the cross sections as given by this parametriza tion already compares favourably with the experiment, a simple extension of the formula leads to an even more accurate description for electron-impact ionization of ions [2]. Using recent results from an extended Wannier theo ry for multiple ionization [3,4], tests of similar parametrizations for mul tiple ionization processes become feasible.