Herbig-Haro objects are emission nebulae formed when outflow from
a YSO impacts on ambient matter, setting up shocks in both the
outflowing and ambient material.  The exact nature of these shocks
is still poorly understood, particularly the relationship between
the shocked atomic and molecular gas.

One of the chief problems is that the shocked atomic and molecular
gas seem to be coincident, despite the fact that the shocks which
excite the atomic gas should dissociate the molecules.  Although
several explanations have been proposed, the question remains
unresolved.

An important clue in the resolution of the puzzle lies in the
observations of shocked molecular hydrogen.  Observations of
hydrogen lines arising from widely varying upper energy states
can map the temperature structure of the cooling shock, and
therefore identify the type of shock.

Unfortunately, the molecular hydrogen lines readily available from
the ground are either very faint, or else span a very narrow range
of upper energy states.  If we are to understand these shocks through
the molecular hydrogen emission we must have observations from a
greater range of lines.  The most important of these "missing" lines
lie in the ISO wavelength range.

We propose to use the CAM to image some of these lines.  The ISO
observations will be compared to ground-based 2um images in order
to map the temperature structure and extent of the shocked gas.