Radiation Damping in the Photoionization of Fe^{14+}

TL;DR

This study uses advanced theoretical methods to analyze the photoionization of Fe^{14+}, revealing the importance of radiation damping and suggesting revisions to existing atomic data for better accuracy in opacity calculations.

Contribution

It extends previous R-matrix calculations by including radiation damping and fine-structure effects, providing more accurate cross sections aligned with experimental data.

Findings

Radiation damping significantly reduces the photoionization cross section.

Computed cross sections agree with experiments after a -3.5 eV energy shift.

Discrepancies in L-shell threshold energies suggest NIST data may be inaccurate.

Abstract

A theoretical investigation of photoabsorption and photoionization of Fe^{14+} extending beyond an earlier frame transformation R-matrix implementation is performed using a fully-correlated, Breit-Pauli R-matrix formulation including both fine-structure splitting of strongly-bound resonances and radiation damping. The radiation damping of $2p\rightarrow nd$ resonances gives rise to a resonant photoionization cross section that is significantly lower than the total photoabsorption cross section. Furthermore, the radiation-damped photoionization cross section is found to be in good agreement with recent experimental results once a global shift in energy of $\approx -3.5$ eV is applied. These findings have important implications. Firstly, the presently available synchrotron experimental data are applicable only to photoionization processes and not to photoabsorption; the latter is required in opacity calculations. Secondly, our computed cross section, for which the L-shell ionization threshold is aligned with the NIST value, shows a series of $2p \rightarrow nd$ Rydberg resonances that are uniformly 3-4 eV higher in energy than the corresponding experimental profiles, indicating that the L-shell threshold energy values currently recommended by NIST are likely in error.