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R. F. Ferrante (U S Naval Academy), M. H. Moore (NASA/Goddard Space Flight Center), J. A. Nuth (NASA/Goddard space Flight Center)
The spectra of adsorbed species, especially thin films, are known to show effects related to the nature of the deposition surface. Subtle effects, such as shifts in line positions, are common, and must be recognized to ensure proper spectral assignments of the deposited material. We have also observed more dramatic effects, including low temperature crystallization (LTC), which appears to be surface-dependent as well. Here, the ice film forms in the crystalline phase at deposition temperatures well below the amorphous-to-crystalline transition point. Since astronomers often use the phase of the deposited ice to give important clues about the thermal- and radiation-history of the object, a better understanding of the effect of the surface on the spectrum of the deposited ice is required. To that end, we have measured a number of surface properties (surface area, pore volumes, and pore size distributions) for a variety of amorphous silicate interstellar grain analogs, and have studied the IR spectra of methanol (and other ices) deposited on these materials. Thermally induced modifications to some of these surfaces have also been examined. Results and correlations among the data will be presented.