Formation Pumping of Molecular Hydrogen in Dark Clouds
  Many theoretical and laboratory studies predict H2 to be formed in highly
excited ro-vibrational states. The consequent relaxation of excited levels via
a cascade of infrared transitions might be observable in emission from suitable
interstellar regions. In this work, we model H2 formation pumping in standard
dense clouds, taking into account the H/H2 transition zone, through an accurate
description of chemistry and radiative transfer. The model includes recent
laboratory data on H2 formation, as well as the effects of the interstellar UV
field, predicting the populations of gas-phase H2 molecules and their IR
emission spectra. Calculations suggest that some vibrationally excited states
of H2 might be detectable towards lines of sight where significant destruction
of H2 occurs, such as X-ray sources, and provide a possible explanation as to
why observational attempts resulted in no detections reported to date.
