  This paper presents a theoretical investigation on the polarization and
magnetic sensitivity of the near-ultraviolet (near-UV) solar spectral lines of
Fe II between 250 and 278 nm. In recent years, UV spectropolarimetry has become
key to uncover the magnetism of the upper layers of the solar chromosphere. The
unprecedented data obtained by the CLASP2 suborbital space experiment across
the Mg II h and k lines around 280 nm are a clear example of the capabilities
of near-UV spectropolarimetry for the magnetic field diagnostics throughout the
whole solar chromosphere. Recent works have pointed out the possible
complementary diagnostic potential of the many Fe II lines in the unexplored
spectral region between 250 and 278 nm, but no quantitative analysis of the
polarization and magnetic sensitivity of those spectral lines has been carried
out yet. To study the polarization signals in these spectral lines, we create a
comprehensive atomic model including all the atomic transitions resulting in
strong spectral lines. We then study the magnetic sensitivity of the linear and
circular polarization profiles in a semi-empirical model representative of the
quiet sun. We present a selection of Fe II spectral lines with significant
linear and circular polarization signals and evaluate their diagnostic
capabilities by studying their formation heights and magnetic sensitivity
through the action of the Hanle and Zeeman effects. We conclude that when
combined with the CLASP2 spectral region these Fe II lines are of interest for
the inference of magnetic fields throughout the solar chromosphere, up to near
the base of the corona.

Solar and Stellar Astrophysics