R=100,000 Spectroscopy of Photodissociation Regions: H2 Rotational Lines   in the Orion Bar
  Ground state rotational lines of H2 are good temperature probes of moderately hot (200-1000 K) gas. The low A-values of these lines result in low critical densities while ensuring that the lines are optically thin. ISO observations of H2 rotational lines in PDRs reveal large quantities of warm gas that are difficult to explain via current models, but the spatial resolution of ISO does not resolve the temperature structure of the warm gas. We present and discuss high spatial resolution observations of H2 rotational line emission from the Orion Bar. 
Katelyn N. Allers, Daniel T. Jaffe, John H. Lacy, Matthew J. Richter