Extended scaling of cross-sections for the ionization of H, H2 and He by multiply charged ions

An analytic cross-section formula is given for the impact ionization of H, H2 and He by multiply charged ions. The formula is expressed as a modified Bethe cross-section for ionization by protons, multiplied by the square of the ionic charge and an analytic scaling factor. This scaling factor behaves as Eν at low energies, where E represents the projectile energy and ν is approximately equal to 0.9. The values of adjustable parameters in the formula were determined by least squares fits to the experimental data collected from the literature. The lowest projectile energy of the available data is 6 keV/amu and the root mean square deviation of all data from the analytic formula is 21%. (author). 19 refs, 2 figs, 3 tabs