Key points are not available for this paper at this time.
Low-resolution spectra have been obtained for a selection of infrared protostars and one object located behind the Taurus dark cloud. Most of the differences in the spectra can be attributed to different H2O ice temperatures combined with additional broad absorption between 3.3 and 3.5 microns plus another absorption in the 2.8-2.9 micron range. An NH3-H2O ice mixture, scattering by H2O ice-coated grains, and hydrated silicates are ruled out as explanations for the last type of absorption. The most plausible explanation is still some form of hydrocarbon in the grain mantles.
Smith et al. (Fri,) studied this question.