Laboratory confirmation and improved Accuracy of 4f and 5d energy levels of Fe II previously identified from stellar spectra

TL;DR

This study confirms and refines 24 energy levels of Fe II using laboratory spectroscopy, significantly improving their accuracy for astrophysical applications.

Contribution

It provides the first laboratory confirmation of 24 Fe II energy levels, enhancing the precision of atomic data used in astrophysics.

Findings

24 Fe II energy levels confirmed in laboratory for the first time.

Energy and wavelength uncertainties reduced by up to an order of magnitude.

Results support more reliable astrophysical spectral analyses.

Abstract

Many energy levels of singly ionised iron (Fe II, $Z=26$) remain uncertain or experimentally unknown. Their identification and spectral line data are required in reliable astrophysical spectral analyses. In motivation for improving the atomic data of Fe II, we analysed emission spectra of a Fe-Ne plasma produced by a Penning discharge lamp recorded by high-resolution Fourier transform spectroscopy in the region 9000-27,000 cm$^{-1}$ (11,111-3704 {\AA}). Semi-empirical transition probability calculations and stellar spectra of Fe II were used to guide the analysis. In total, 24 energy levels of the 3d$^6$4f and 3d$^6$5d configurations of Fe II lying between 122,351-127,881 cm$^{-1}$ were confirmed in the laboratory for the first time, in agreement with their identities proposed by previous investigations involving only stellar spectra. Level energy and wavelength uncertainties of the 24 levels are improved by up to an order-of-magnitude compared to previously published values. These results will enable more reliable application of Fe II in astrophysical spectroscopic analyses and support further investigations of the spectrum and energy levels of Fe II.