  The Ba II D2 line at 4554 A is a good example, where the F-state interference
effects due to the odd isotopes produce polarization profiles, which are very
different from those of the even isotopes that do not exhibit F-state
interference. It is therefore necessary to account for the contributions from
the different isotopes to understand the observed linear polarization profiles
of this line. In this paper we present radiative transfer modeling with partial
frequency redistribution (PRD), which is shown to be essential to model this
line. This is because complete frequency redistribution (CRD) cannot reproduce
the observed wing polarization. We present the observed and computed Q/I
profiles at different limb distances. The theoretical profiles strongly depend
on limb distance (\mu) and the model atmosphere which fits the limb
observations fails at other \mu\ positions.
