The shock reaction of molecular clouds to the supersonic outflows
from embedded young stars is being studied. Notable observable
consequences include (1) extensive bipolar eruptions of cool
high-momentum material surrounding or adjacent to (2) compact
regions of hot shocked gas. The hot gas can be observed with ISO
in the lines of vibrationally-excited molecular hydrogen.
Strong lines are expected in the range 5-10 microns which
originate from transitions within each vibrational level. None
of these lines have ever been observed in interstellar gas.
Therefore, success here would establish a new path for
investigating the nature of hot molecular gas in general.
Advanced shock modelling of existing data demonstrate that these
are easily measurable in some objects and are of special
diagnostic value. The SWS would perform here individual
observations of a group of four lines between 4.9 and 6 mu.
     The data will provide a tight link between components (1) and
(2) noted above. This link has been problematic with ground-based
observations especially for embedded stars. The expected higher
transparency offered by ISO will enable us to determine
whether or not the CO-deduced momentum can be jet or wind driven.
This will be derived from the intrinsic power of the shock. The
line ratios will inform us of how the shock operates - whether
rapid heating, gradual dissociation, water cooling etc. -
which could provide basic knowledge of the materials from
which stars form. To this purpose, the lines and sources are
chosen so that excitation temperatures and column densities
can be derived extremely accurately and related to the nature
of the source.