New Fe I Level Energies and Line Identifications from Stellar Spectra.
  III. Initial Results from UV, Optical, and Infrared Spectra
  The spectrum of neutral iron is critical to astrophysics, yet furnace
laboratory experiments cannot reach many high-lying Fe I levels. Instead,
Peterson & Kurucz (2015) and Peterson, Kurucz & Ayres (2017) turned to UV and
optical spectra of warm stars to identify and assign energies for 124 Fe I
levels with 1900 detectable Fe I lines, and to derive astrophysical gf-values
for over a thousand of these. An energy value was assumed for each unknown Fe I
level, and confirmed if it shifted the predicted positions in updated Kurucz
(2011) Fe I calculations to match exactly in wavelength the positions of four
or more unidentified lines in the observed spectra. Nearly all these
identifications were for LS levels characterized by spin-orbit coupling, whose
lines fall primarily at UV and optical wavelengths. This extension of these
searches provides a hundred new Fe I level identifications. Forty LS levels are
identified largely by incorporating the positions of unidentified laboratory Fe
I lines with wavelengths < 2000A. Adding infrared spectra provided sixty Fe I
jK levels, where a single isolated outer electron orbits a compact core. Their
weak, blended lines fall mostly in the infrared, but are searchable because
their neighboring energies obey tight relationships. For each new Fe I level,
this work again provides and makes publicly available its identification, its
energy, and a list of its lines with theoretical gf values. For suitably
distinct lines, this work also includes astrophysical gf-values, ones adjusted
semi-empirically to fit the stellar spectra.
