THE SPECTRUM OF Fe II

The spectrum of singly ionized iron (Fe ii ) has been recorded using high-resolution Fourier transform (FT) and grating spectroscopy over the wavelength range 900 Å to 5.5 μm. The spectra were observed in high-current continuous and pulsed hollow cathode discharges using 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 μm to 0.05 cm −1 for weaker lines around 1500 Å. The wavelength uncertainty of lines in the grating spectra is 0.005 Å. The ionization energy of (130,655.4 ± 0.4) cm −1 was estimated from the 3d 6 ( 5 D)5g and 3d 6 ( 5 D)6h levels.