Ultraviolet radiation inside interstellar grain aggregates. II. Field depolarization

We study the polarization of the UV light within the cavities of interstellar grain aggregates modeled as homo- geneous spheres containing several spherical voids. The incident field is a linearly polarized plane wave. We found that field depolarization occurs in all examined cases so that the field within the cavities has the features of an ellip- tically polarized wave. The depolarization of the field does not depend on the material of the grains but on the geometry of the problem only. The implications of this result for the interstellar photochemistry are briefly discussed.