1994A&AS..103...45M

We have measured the far-infrared spectra of pure H₂O, CH₃OH, NH₃, CO₂, H₂CO, CH₄, and CO ices and H₂O-dominated binary mixtures of CH₃OH, NH₃, CO₂, H₂ CO, CH₄, and CO from 500cm^–1 (20µm) to 100cm^–1 (100µm) at low temperatures. We also examined spectra of several more complex ices. These results represent a consistent set of data on astrophysically relevant molecules and mixtures over a wide range of temperatures. This set provides information in a spectral region that will be increasingly accessible with the advent of future orbiting observatories. Spectra of both the amorphous and crystalline phases of each of the pure molecular ices are unique. Spectra of icy mixtures, however, are in general dominated by H₂O ice features over the entire range of temperatures studied. One exception to this is the H₂O+CH₃ OH ice which evolves from an amorphous deposit to form a multi-line crystalline-like spectrum we have identified with the recently reported CH₃OH clathrate hydrate. Implications of these results on the identification of extraterrestrial ices based on observations in the far-infrared are included.