Some 'solid facts' on interstellar dust

Despite considerable observational information on infrared absorption and emission spectra of interstellar matter, together with extensive laboratory data on the spectra of possible constituents, there are presently few firm identifications of individual chemical components. Simple chemical compounds including H2O, CO and CO2 are detected in dust in dark interstellar clouds, but other molecules such as ethane, acetylene and benzene do not appear to be present with appreciable abundance. Nevertheless, IR spectra show that hydrocarbons are a ubiquitous component of interstellar matter. The nature of these materials and their relation to specific molecular components is discussed in this paper.