Towards Complete Microphysical Modeling of Warm Interstellar Molecules: H2 Collisional Dissociation for Spitzer IR Observations

Details Towards Complete Microphysical Modeling of Warm Interstellar Molecules: H2 Collisional Dissociation for Spitzer IR Observations Towards Complete Microphysical Modeling of Warm Interstellar Molecules: H2 Collisional Dissociation for Spitzer IR Observations

May 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006sptz.prop30063f&link_type=abstract

Spitzer Proposal ID #30063

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The role of molecules in a variety of interstellar environments, including photodissociation regions, star-forming regions, circumstellar shells, and other molecular regions, is far-reaching. Molecules are pivotal to determining the thermal and density structure of the gas and provide diagnostics through emission, absorption, and fluorescence. However, these environments are typically of low density, may be exposed to shocks, and are usually irradiated in the UV by nearby hot stars which results in significant departures from equilibrium for the chemical, ionization, and internal energy state of the gas. Therefore, to accurately model these environments, and thereby interpret results from Spitzer spectroscopic observing programs, requires a quantitative understanding of a variety of microphysical processes. We propose here to focus our studies on the most abundant of molecules, H2. To derive significant scientific return from current and future Spitzer observations, we will compute dissociation rate coefficients of H2 due to collisions of H, He, para-H2, and ortho-H2, a process which is competitive with other H2 destruction mechanisms. The rate coefficients will be computed for temperatures between 1 and 50,000 K and from ALL initial bound rotational-vibrational levels of H2 in the ground electronic state, information which is unavailable today. The computations will be performed using established quantum mechanical close-coupling and coupled-states methods on accurate, and well tested, potential energy surfaces. The results will be benchmarked against experiment, where available, and fit to analytic forms with physical low- and high-temperature limits for easy modeling use. The results of this proposal will then enable models, such as those from the widely used and tested spectral synthesis code Cloudy, to reliably simulate H2 in molecular environments, leading to deeper examination and understanding of their physical properties through Spitzer observations.

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