Paper SS-TuP12
CO₂ Optical Phonons for Constraining Mixing in Interstellar Ices

Tuesday, November 8, 2016, 6:30 pm, Room Hall D

CO₂ is an important ice species in interstellar environments, often the second most abundant ice after H₂O. Astronomical infrared spectra of interstellar objects have revealed abundant CO₂ in a variety of protostellar environments as well as in cold dark clouds. The CO₂ ν₂ band has been used as a tracer of thermal processing due to its dependence on the ice temperature and local environment; however, there are still uncertainties involved in fitting the laboratory v₂ band to astronomical spectra. We report laboratory spectra of the CO₂ longitudinal optical (LO) phonon mode for a series of CO₂ ices at low temperature and for ice mixtures with polar (H₂O) and non-polar (CO, O₂) components. We show that the LO phonon mode is particularly sensitive to the mixing ratio of various ice components of astronomical interest. These spectra may be useful in constraining the bulk environment of CO₂ in astronomical ices as well as for tracing ice mixing in laboratory experiments.