Identification of interstellar polysaccharides and related hydrocarbons

Abstract

INFRARED transmittance spectra of several polysaccharides which are suitably calibrated for comparison with astronomical data have been obtained. We show here that a mean 2.5–15 µm spectrum computed from our measurements is remarkably close to that required to explain a wide range of astronomical data, except for two significant points of departure. The required relative opacity at the 3 µm absorption dip is a factor ∼1.5 lower than we found in our laboratory measurements: this difference may arise from the presence of water (∼ 10%) associated with terrestrial polysaccharide samples. In the 9.5–12 µm waveband an additional source of opacity seems to be necessary. The close agreement between the spectrum of this excess opacity and the absorption spectrum of propene C₃H₆ points strongly to the identification of hydrocarbons of this type which may be associated with polysaccharide grains in interstellar space.