2013 Articles

Storage Ring Cross Section Measurements for Electron Impact Single and Double Ionization of Fe13+ and Single Ionization of Fe16+ and Fe17+

Hahn, M.; Becker, A.; Bernhardt, D.; Grieser, M.; Krantz, C.; Lestinsky, M.; Müller, A.; Novotný, O.; Repnow, R.; Schippers, S.; Spruck, K.; Wolf, A.; Savin, Daniel Wolf

We report measurements of electron impact ionization for Fe13+, Fe16+, and Fe17+ over collision energies from below threshold to above 3000 eV. 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 Fe13+, 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 is more than 30% larger, while that of Dere 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 Fe13+ is dominated by direct ionization of an inner shell electron accompanied by autoionization of a second electron. Our results for single ionization of Fe16+ and Fe17+ agree with theoretical calculations to within the experimental uncertainties.