  We present new calculations for transition probabilities of Fe IV, with much
more extensive datasets than heretofore available. The large-scale close
coupling R-matrix calculations yield 1,798 LS bound states with n $\leq$ 11 and
$l \leq$ 9, and corresponding transition probabilities for 138,121 dipole
allowed transitions in the form of oscillator strengths $f$, line strengths
$S$, and A-coeffficients for a variety of applications. This represents the
largest R-matrix dataset in LS coupling for any ion under either the Opacity
Project or the Iron Project. Through algebraic transformation of the LS
multiplets, a total of 712,120 dipole allowed fine structure transitions for Fe
IV are obtained. Observed transition energies are used together with the energy
independent line strengths to derive the $f$- and the $A$-values; the adopted
algorithm used calculated energies for the remainder. Present results show
significantly better accuracy for the important low-lying states than previous
calculations. Monochromatic and mean opacities for Fe IV are computed and
compared with those obtained using the Opacity Project data. We find
differences which could have important consequences for several astrophysical
applications involving low ionization stages of iron.
