Relativistic distorted-wave cross sections are calculated for electron-impact ionization from the 21 subshells with n=3, 4, and 5 in several types of ions. Based on these results and the general, but very simple form for the cross section derived by Sampson and Zhang [Phys. Rev. A 45, 1657 (1992)] a very rapid, but quite accurate method using fits to the reduced cross sections is given. This applies to highly charged ions with any degree of complexity and should be very convenient for use in plasma modeling. The procedure is illustrated by application to inner-shell ionization of Cu-like gold ions, where good agreement is obtained with detailed direct relativistic distorted-wave calculations.

• Received 30 March 1993

DOI:https://doi.org/10.1103/PhysRevA.48.1975