Assigned ID: 193 ----- Attempting Submission 1 (Thu Mar 06 20:57:18 GMT 2008) ----- With the upcoming servicing of the HST and the installation of COS, a large number of molecular absorption and emission features will be observable in the visible and ultraviolet. These observations, and analysis of past ones, are expected to give new insights into our understanding of the evolution of a range of astronomical sources and the chemistry occuring in these environments. In particular, molecules are primarily destroyed in diffuse and translucent regions via photodissociation (PD) due to incident UV and optical radiation. The majority of astrochemical/spectral modeling codes available today use pre-computed exponentially-attenuated photorates based on dust scattering/absorption for an ``average" interstellar cloud. Since there is clearly a large scatter in the dust properties and local radiation field for various environments in the Galaxy and beyond, the adoption of such pre-computed photorates can lead to considerable errors in predicted abundances. We propose here to significantly improve current modeling capabilities by computing new rovibrationally-resolved PD cross sections for C_2, CN, and CS; constructing a publicly available database of available PD cross sections; implementating the PD cross sections into the spectral simulation code Cloudy for explicit computation of local photorates; and testing of the Cloudy implementation in diffuse and translucent cloud simulations and with photodissociation region benchmark models. The successful completion of the goals from this proposal will be important for obtaining accurate molecular abundances from HST observations of diffuse clouds, translucent clouds, and other UV-irradiated molecular regions and in inferring local grain properties.

ISM AND CIRCUMSTELLAR MATTER 12 74156 false 0.0 0.0 false false true false false SUPPORTED