  The spectra of B-type and early A-type stars show mumerous unidentified lines
in the whole optical range, especially in the 5100-5400 A interval. Because Fe
II transitions to high energy levels should be observed in this region, we used
semiempirical predicted wavelengths and gf-values of Fe II to identify unknown
lines. Semiempirical line data for Fe II computed by Kurucz are used to
synthesize the spectrum of the slow-rotating, Fe-overabundant CP star HR 6000.
We determined a total of 109 new 4f levels for Fe II with energies ranging from
122324 cm^-1 to 128110 cm^-1. They belong to the Fe II subconfigurations
3d^6(^3P)4f (10 levels), 3d^6(^3H)4f (36 levels), 3d^6(^3F)4f (37 levels), and
3d^6(^3G)4f (26 levels). We also found 14 even levels from 4d (3 levels), 5d (7
levels), and 6d (4 levels) configurations. The new levels have allowed us to
identify more than 50% of the previously unidentified lines of HR 6000 in the
wavelength region 3800-8000 A. Tables listing the new energy levels are given
in the paper; tables listing the spectral lines with log gf >/= -1.5 that are
transitions to the 4f energy levels are given in the Online Material. These new
levels produce 18000 lines throughout the spectrum from the ultraviolet to the
infrared.
