Electron-Impact Ionization Cross-Sections and Ionization Rate Coefficients for Atoms and Ions

Abstract

All available experimental data on cross-sections for single ionization of atoms and ions from the ground state by electron impact in the low-energy range (< 10 keV) have been collected. For each species a best-fit curve has been drawn. The experimental results can be approximated by the following formulae: a lfl(E/Xi)[cm2], if xi<E<x23 N aln(EIxi) -aln(E!k) XE kE ` if E>xN, where Xi is the ionization potential for electrons in the outermost shell in electron-volts, X2 is the ionization potential for electrons in the next inner (sub) -shell, etc., x is a weighted mean of xi and Xi, etc., E is the electron energy in electron-volts, a = 4.0 X ; > 0.5 is a slowly varying function and asymptotically equal to the number of equivalent electrons. In most cases it is sufficient to set N equal to 2, but for Kr and Xe N = 3 gives better results. By comparison of isoelectronic species as well as of equally charged species it is possible to make predictions for yet unknown cross-sections. Ionization rate coefficients for all species in the triangle H i-Na i-Na xi are given with an estimated error of +- per cent.