Ultraviolet spectra of organic molecules and the interstellar medium

Abstract

THE polysaccharides cellulose and starch have been shown to give an excellent match to certain spectra of the interstellar medium¹. The matching was based on comparisons of the laboratory spectra of polysaccharides in the 2–30-µm region with those of various astronomical objects, in particular dark clouds near the Trapezium^2,3. Cellulose has broad absorption bands at 3, 10 and 20 µm devoid of the 10.3-µm high transmittance spike reported for crystalline silicates⁴, the commonly accepted dominant interstellar material. It has been claimed that cellulose obviates the need for the presence of both H₂O ice and silicates in the interstellar medium¹. Several organic molecules have already been found associated with dust grains in the interstellar medium. The dust grains offer protection from dissociation and could aid in the cellulose formation process⁵ The ultraviolet (UV) absorption in the interstellar medium can provide an additional identification technique for interstellar organic molecules, and this poses the question as to what are the UV spectral characteristics of cellulose. We have tried to answer this question by measuring the UV spectrum of cellulose between 0.19 and 0.40 µm, and comparing to the observed UV spectrum of the interstellar medium⁶. The sample we chose was regenerated cellulose produced from wood pulp, known generally as cellophane.