Electron Impact Ionization of Multicharged Ions

The available literature on electron impact ionization of ions of charge + 3 or greater is reviewed. Several easily used formulae are presented-the classical result, the Lotz formula, and a scaled Coulomb-Born prescription. The available experimental cross-sections, which now include a few good quality crossed-beams measurements, are compared with the cross-sections obtained from the formulae and, where available, with true Coulomb-Born calculations. The Lotz formula is overall found to be closest to the experimental results. However, this result is fortuitous since much of the experimental data are found to contain measurable contribution from the excitation-autoionization process not included in any of the formulae. It appears to be more important to include estimates of the excitation-autoionization contribution to ionization cross-sections than to improve the models of the direct ionization process.