Cool Interstellar Physics and Chemistry

The infrared (IR) spectra of molecular cloud material in the interstellar medium of galaxies are dominated by absorption features due to simple molecules such as H 2 O, CH 3 OH, NH 3 , CO 2 , and CO in cryogenic molecular ices. These ices are an important reservoir of material and play an important role in the organic inventory of regions of star and planet formation. Observational studies have revealed the presence of several independent ice components, often along the same line of sight. These interstellar ices are formed by accretion and reaction on grain surfaces and further processed by ultraviolet (UV) photons as well as highly energetic cosmic ray ions. Thermal processing by nearby newly formed stars is also important. In this chapter, we will review the characteristics, formation, and evolution of interstellar ices with the emphasis on relevant laboratory studies in the area of IR spectroscopy of low-temperature molecular mixtures, the surface chemistry of simple species relevant to astrophysical environments, and analog studies of the energetic processing of ices near newly formed stars.