Very High Excitation Lines of H$_{2}$ in the Orion Molecular Cloud
  Outflow
  Vibration-rotation lines of H$_{2}$ from highly excited levels approaching
the dissociation limit have been detected at a number of locations in the
shocked gas of the Orion Molecular Cloud (OMC-1), including in a Herbig-Haro
object near the tip of one of the OMC-1 "fingers." Population diagrams show
that while the excited H$_{2}$ is almost entirely at a kinetic temperature of
$\sim$1,800 K, (typical for vibrationally shock-excited H$_{2}$), as in the
previously reported case of Herbig-Haro object HH 7 up to a few percent of the
H$_{2}$ is at a kinetic temperature of $\sim$5,000~K. The location with the
largest fraction of hot H$_{2}$ is the Herbig-Haro object, where the outflowing
material is moving at a higher speed than at the other locations. Although
theoretical work is required for a better understanding of the 5,000 K H$_{2}$,
(including how it cools), its existence and the apparent dependence of its
abundance relative to that of the cooler component on the relative velocities
of the outflow and the surrounding ambient gas appear broadly consistent with
it having recently reformed. The existence of this high temperature H$_{2}$
appears to be a common characteristic of shock-excited molecular gas.
