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R. Mohr, P. Gerakines, D. Alvarez, H. Polhill (University of Alabama Birmingham)
Infrared observations of dense interstellar clouds reveal a variety of condensed volatiles (ices) that coat the surfaces of interstellar dust grains in a thin (0.01 to 0.10 micrometer) icy grain mantle. It has also been shown that the overall gas-phase chemistry of these clouds is intimately linked to the chemistry of the mantles. This requires either formation of certain molecules (water and carbon dioxide, for example) to take place either by surface catalysis or by photochemistry. The latter can be driven by the UV radiation from stars or induced by the cosmic-ray ionization of interstellar hydrogen.
In this poster, we present preliminary results from a computer simulation of the bulk UV photolysis of interstellar icy grain mantles. These initial simulations consider only the dissociation of molecules by the UV photons (water is broken down into OH and H, for example). Second generation simulations also consider reactions of these dissociation products with other species in the icy mantle to form new species (photolysis of water may eventually produce hydrogen peroxide, for example). Future versions of the code will have several additional modifications including the ability to handle both homogeneous and heterogeneous initial ice matrices.
Once the code has been fully developed, the output of these simulations will be compared to laboratory UV photolysis experiments in order to determine the actual reactions' branching ratios and reaction rates. Ultimately, we will apply these results to simulations of interstellar icy grain mantles of appropriate geometries and compositions and couple them to gas-phase models in order to develop a more complete simulation of the coupling of gas and grain chemistries.
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Bulletin of the American Astronomical Society, 37 #2
© 2005. The American Astronomical Soceity.