  Supernovae of type IIn possess spectral signatures that indicate an intense
interaction between the supernova ejecta and surrounding dense circumstellar
material cast off by the star in pre-explosion mass-loss episodes. Studying
this interaction can yield clues to the nature of Type IIn progenitors and
their mass loss history. In particular, polarization spectra of Type IIn's show
complex line polarization and position angle features that arise from a
combination of geometrical and optical effects. I have constructed a Monte
Carlo code that simulates the transfer of the H alpha line through
circumstellar shells with various geometrical configurations and optical
characteristics. The superposition of broad and narrow line components produced
in different regions of the circumstellar environment and modified by electron
and line scattering, hydrogen absorption, thermal emission, and geometrical and
viewing angle effects gives rise to a variety of polarized line shapes in the
model spectra. Comparison of these results with recent high-quality
spectropolarimetric observations of Type IIn supernovae suggests that a model
"shock" region between the supernova photosphere and the circumstellar shell is
necessary to produce the narrow polarized emission features at the rest
wavelength of H alpha seen in some IIn's. Further model results point toward
other features in the polarized line profile that can be used to constrain the
characteristics of the circumstellar material in these intriguing objects. The
code's usefulness will be extended by the treatment of Doppler effects due to
expansion of the circumstellar scattering region, such as those that
characterize the polarized H alpha profiles of the Type IIn SN 1997eg.
