Description
We report measurements of electron impact ionization for Fe^13+^, Fe^16+^, and Fe^17+^ over collision energies from below threshold to above 3000eV. The ions were recirculated using an ion storage ring. Data were collected after a sufficiently long time that essentially all the ions had relaxed radiatively to their ground state. For single ionization of Fe^13+^, we find that previous single pass experiments are more than 40% larger than our results. Compared to our work, the theoretical cross section recommended by Arnaud & Raymond (1992ApJ...398..394A) is more than 30% larger, while that of Dere (2007, J/A+A/466/771) is about 20% greater. Much of the discrepancy with Dere is due to the theory overestimating the contribution of excitation-autoionization via n=2 excitations. Double ionization of Fe^13+^ is dominated by direct ionization of an inner shell electron accompanied by autoionization of a second electron. Our results for single ionization of Fe^16+^ and Fe^17+^ agree with theoretical calculations to within the experimental uncertainties.
|