Other indirect ionization channels, such as EMA, have been neglected. We note, though that in many cases these other indirect contributions are, fortuitously, roughly accounted for in the semiempirical formulae. This is because the fitting parameters used in the formulae were usually estimated without attempting to distinguish direct and indirect channels, except for IA. Below, we discuss in more detail the experimental measurements and formulae used for each EIMI cross section in our calculations.

In the following, the direct EIMI thresholds are generally from @NIST:2013, while the thresholds for ionization of core electrons come from @Kaastra:AAS:1993 unless otherwise noted. The ionization thresholds for $K$-shell ionization of a core electron are an order of magnitude greater than any other relevant thresholds, being $\gtrsim7000$ eV. Thus $K$-shell IA contributes significantly to the EIMI rate coefficient at temperatures $\gtrsim10^{8}$ K. In most cases, these contributions are included using the Lotz-formula scaled by the branching ratios, i.e., Equation (\[eq:lotz\]). However, it is worth noting that this approximation ignores relativistic effects, which may become important at such high energies. In particular, at high energies the Lotz formula cross section falls off like $\ln(u)/u$ as predicted by the Bethe approximation, but in the relativistic limit the 