INFRARED SPECTRA OF AMMONIA-WATER ICES

We conducted a systematic study of the near-IR and mid-IR spectra of ammonia-water ices at various NH3/H2O ratios. The differences between the spectra of amorphous and crystalline ammonia-water ices were also investigated. The 2.0 mu m ammonia band central wavelength is a function of the ammonia/water ratio. It shifts from 2.006 +/- 0.003 mu m (4985 +/- 5 cm(-1)) to 1.993 +/- 0.003 mu m (5018 +/- 5 cm(-1)) as the percentage of ammonia decreases from 100% to 1%. The 2.2 mu m ammonia band center shifts from 2.229 +/- 0.003 mu m (4486 +/- 5 cm(-1)) to 2.208 +/- 0.003 mu m (4528 +/- 5 cm(-1)) over the same range. Temperature-dependent shifts of those bands are below the uncertainty of the measurement, and therefore are not detectable. These results are important for comparison with astronomical observations as well as for estimating the concentration of ammonia in outer solar system ices.