Molecular Hydrogen in Star-forming regions: implementation of its   micro-physics in Cloudy
  Much of the baryonic matter in the Universe is in the form of H2 which includes most of the gas in galactic and extragalactic interstellar clouds. Molecular hydrogen plays a significant role in establishing the thermal balance in many astrophysical environments and can be important as a spectral diagnostic of the gas. Modeling and interpretation of observations of such environments requires a quantitatively complete and accurate treatment of H2. Using this micro-physical model of H2, illustrative calculations of prototypical astrophysical environments are presented. This work forms the foundation for future investigations of these and other environments where H2 is an important constituent. 
G. Shaw, G. J. Ferland, N. P. Abel, P. C. Stancil, P. A. M. van Hoof