The Effect of Methane, Ammonia, and Silicates on the 3.07-MICRON Ice Absorption in Interstellar Grains

Laboratory measurements of the infrared spectra of condensed water-ammonia and water-methane mixtures showed no change in the positions of water, ammonia, or methane absorption bands. These results indicate that no hydrogen-bonded water-ammonia or water-methane species were produced. In the water-methane experiments, the relative intensities of the 2.8- and 6.2- absorptions due to monomeric water were reversed, but no other changes occurred. Water adsorbed on various silicates also shows absorption near 3.0 which is shifted outside the atmospheric absorption with little change in band shape. There is no apparent explanation of the absence of an interstellar 3.07- band if the water concentration is more than about 15 percent. For water concentrations up to about 5 percent the strongest bands fall in the 2.7-3.0- region. Therefore, astronomical observations in this spectral region are needed.