The spectrum of Fe II

TL;DR

This study provides a comprehensive high-resolution spectral analysis of Fe II, classifying nearly 13,000 lines and determining precise energy levels and ionization energy, significantly advancing atomic data for this ion.

Contribution

The paper presents an extensive high-resolution spectral dataset for Fe II, including classification of 12,900 lines and refined energy levels, using multiple spectroscopic techniques.

Findings

Classified approximately 12,900 Fe II lines.

Optimized 1027 energy levels with measured wavenumbers.

Estimated ionization energy of Fe II as 130,655.4±0.4 cm⁻¹.

Abstract

The spectrum of singly-ionized iron (Fe II) has been recorded using high-resolution Fourier transform and grating spectroscopy over the wavelength range 900 {\AA} to 5.5 {\mu}m. The spectra were observed in high-current continuous and pulsed hollow cathode discharges using Fourier transform (FT) spectrometers at the Kitt Peak National Observatory, Tucson, AZ and Imperial College, London and with the 10.7 m Normal Incidence Spectrograph at the National Institute of Standards and Technology. Roughly 12 900 lines were classified using 1027 energy levels of Fe II that were optimized to measured wavenumbers. The wavenumber uncertainties of lines in the FT spectra range from 10-4 cm-1 for strong lines around 4 {\mu}m to 0.05 cm-1 for weaker lines around 1500 {\AA}. The wavelength uncertainty of lines in the grating spectra is 0.005 {\AA}. The ionization energy of (130 655.4+-0.4) cm-1 was estimated from the 3d6(5D)5g and 3d6(5D)6h levels.