Unfolding the Information of the Interstellar H$_2$ Spectrum: Its Impact on Spitzer IR Observation

Molecular hydrogen is the most ubiquitous molecule in the universe. H$_2$ plays a pivotal role in a variety of processes that significantly influence the chemical and physical state ofinterste1lar gas. However, the lack of both accurate and complete collisional data sets for rovibrational inelastic cross sections and rate coefficients for H, He, and HS_2S impacting the dominant molecular species (e.g. H$_2$, HD, and CO) has created a serious set back in the development of reliable astrophysical models complementing NASA's {it Spitzer} IR observations, It has been shown that the uncertainties in the existing collisional rate coeftJcient data can be significant. Modeling and interpretation of observations of such emironments require quantitatively accurate and complete treatment ofH$_2$. To derive significant scientific return from the unprecedented observations that are expected in the near future, we propose to compute rovibrational excitation and dissociation cross sections and rate coefficients for collisions ofH, H$_2$ and He with H$_2$ and HD for a1l transitions between a1l bound rovibrationallevels of the target molecules using continued development of well established quantum mechanical close-coupling and classical trajectory methods. Rate coet1lcicnts will bc computed from 10 to 50,000-K and fit to convenient functional forms with phvsical low- and high-temperature limits. The results of this proposal will then enable models, such as the very widely used and tested spectral modeling code Cloudy, to reliably simulate these astrophysical environments, leading to deeper examination