Photoionization Study of Iron-Group Elements (Fe, Co, and Ni): Comparison of Theory and Experiment

Photoionization (PI) of iron-group elements (Fe, Co, and Ni) is investigated in this article in the framework of the screening constant per unit nuclear charge (SCUNC) method. The resonance energies of several series of autoionizing Rydberg resonances identified in the PI spectra of these three transition elements are reported. The results of the SCUNC calculations in this study, which is considered to be the first theoretical study, are compared with the available experimental data and show minimal deviation of the theoretically calculated values from the experimental data. The correspondences obtained are very satisfactory, clarifying the uncertain resonance energies measured for certain series. This comparison reinforces confidence in the available experimental and theoretical data, as well as in the new data extrapolated in this study for astrophysical applications. The theoretical data for iron, cobalt and nickel presented in this work make a significant contribution to improving the fundamental atomic database of transition elements, providing valuable references for future calculations and potential astrophysical applications.