Calculated Coulomb-Born exchange cross sections for hydrogenic ions from 1s through 6h exist in the literature. In this paper, an analytic fit formula to these cross sections is derived by fitting simultaneously to n, l, and u where n is the principal quantum number, l is the orbital angular momentum, and u is the impact electron energy in threshold units. The resulting fit, which is easily integrated over a Maxwellian velocity distribution, reproduces the calculated cross sections to better than 10 percent. A prescription is given for applying the cross sections to nonhydrogenic ions. In addition, the cross sections differential with respect to the energy of the scattered electron are fitted.
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Clark et al. (1991) studied this question.