Infrared properties of isolated water ice.
Abstract
Water ice is the most important component in astrophysical ices and is characterized by a strong broad absorption at 3μm, observed in many interstellar spectra. In specific interstellar environments grain mantles might contain only a small amount of water, which is diluted in other volatiles dominant in these regions (e.g. CO, O_2_, N_2_, CO_2_). Theoretical models suggest that interstellar mantles are rich in non-detected molecules such as O_2_ and N_2_. If water is diluted in non-polar matrices the water molecules display very sharp discrete bands due to the monomeric and dimeric H_2_O. These peculiar bands lie between 2.5 and 2.9μm, shortward of the 3μm polymeric H_2_O ice band. We have performed a detailed study of the infrared properties of H_2_O diluted in various concentrations and matrices containing Ar, CO, CO_2_, O_2_, N_2_ and naphthalene. Each molecule present in the matrix has its individual fingerprint in the spectrum of isolated H_2_O and can be traced by the resulting band position of the individual H_2_O molecules and overall pattern of the infrared spectrum. The concentration of H_2_O in the matrix determines the specific intensity ratios of the monomeric, dimeric and polymeric water bands. We discuss the possible detection of isolated water on low temperature and ultraviolet shielded grain mantles covered with non-polar ices. Together with astronomical spectra taken by the ISO satellite these laboratory data will be extremely valuable for the determination of the grain mantle composition in dense clouds. Due to the unique spectral signature of H_2_O/CO/O_2_ mixtures the detection of isolated water may allow us to infer the presence and abundance of solid O_2_.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- August 1996
- Bibcode:
- 1996A&A...312..263E
- Keywords:
-
- ISM: MOLECULES;
- ISM: ABUNDANCES;
- DUST;
- METHODS: LABORATORY