Theoretical electron-impact-ionization cross section for Fe11+forming Fe12+

Abstract

We have calculated cross sections for electron impact ionization (EII) of P-like Fe${}^{11+}$ forming Si-like Fe${}^{12+}$. We have used the flexible atomic code (FAC) and a distorted-wave (DW) approximation. Particular attention has been paid to the ionization through the $3l\ensuremath{\rightarrow}n{l}^{\ensuremath{'}}$ and $2l\ensuremath{\rightarrow}n{l}^{\ensuremath{'}}$ excitation autoionization (EA) channels. We compare our results to previously published FAC DW results and recent experimental results. We find that the previous discrepancy between theory and experiment at the EII threshold can be accounted for by the $3l\ensuremath{\rightarrow}n{l}^{\ensuremath{'}}$ EA channels which were not included in the earlier calculations. At higher energies the discrepancy previously seen between theory and experiment for the magnitude of the $2l\ensuremath{\rightarrow}n{l}^{\ensuremath{'}}\phantom{\rule{4pt}{0ex}}(n\ensuremath{\ge}4)$ EA remains, though the difference has been reduced by our newer results. The resulting Maxwellian rate coefficient derived from our calculations lies within 11$%$ of the experimentally derived rate coefficient in the temperature range where Fe${}^{11+}$ forms in collisional ionization equilibrium.