A Practical Fit Formula for Ionization Rate Coefficients of Atoms and Ions by Electron Impact: Z = 1-28

Ionization rates for atoms and ions from H to Ni recommended by the Belfast group, supplemented by data derived from several other sources, are fitted to an analytical expression with four fit parameters. On the grounds of its very simple form and its ability to generally replicate the input data to within a few percentage points, we present this expression as a practical formula for use in computer modeling of plasma processes.