  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.
