Level resolved photoionisation cross sections for Fe I

Significant contributions to the UV opacity in the solar atmosphere have been found to stem from bound-free transitions in neutral iron. As such, accurate cross sections for the photoionisation process are required for a detailed and meaningful analysis. However, existing photoionisation cross sections display large discrepancies across the low energy region, highlighting the need for further calculations. In this work we present level resolved photoionisation cross sections for neutral iron across a wide energy range from a 262 level Dirac R-matrix calculation. Comparisons with existing experimental measurements reveal good agreement in the positions of the various low energy resonance features. However, additional comparisons with theoretical datasets highlight wide variations. Significant resonance structures at high photon energies are explored by employing an additional series of 262 level and 896 level Dirac R-matrix calculations with a smaller 6 configuration target. The resulting photoionisation cross sections reproduce the main features from existing experimental observations. The results presented throughout will be useful to those requiring an extensive set of level resolved photoionisation cross sections for astrophysical applications.