We propose to determine the distribution of warm molecular gas in a variety of
Galactic sources.  Using the SWS, we will partially map the emission in the
0-0 S(1) and S(5) lines of the hydrogen molecule in
sources which have strong shocked or fluorescent near-IR H2 line emission.
This allows us to study a regime of parameter space, warm molecular gas at
100-200K, for the first time with a probe arising from the bulk of the gas
present, a ground state transition of the hydrogen molecule. At temperatures
as low as 100K the 0-0 S(1) line is the strongest line of H2,
and considerably easier to observe than the 0-0 S(0) line.
Much of the gas in molecular clouds, outside of dense cores, is at these
temperatures. It is in the form of PDRs, heated by the ambient interstellar
radiation field. We predict detectable levels of 0-0 S(1) line emission from
PDRs. The shock-excited emission from the 0-0 S(1) line is also predicted
to be more extensive than the near-IR lines, as it can be excited in lower
velocity shocks, down to ~5 km/s, than the higher excitation lines.
In addition, the ratio of the 0-0 and 1-0 S(1) lines depends sensitively
on the shock model and the environment of the cloud, and thus will
provide a diagnostic to test competing models. Since comprehensive
mapping is impracticable, our strategy is to make partial
maps of a number of different types of source, concentrating on the brightest
peaks of H2 emission, making cross cuts along and across ridges of emission,
and observing where we have KAO data on other tracers, such as OI and CII.
We will combine these data with an extensive data base on near-IR H2 lines
we have collected, and with models of the H2 emission in shocks and PDRs we
have constructed, to build a picture of the excitation of molecular hydrogen
across the entire energy spectrum of the ground electronic state. We seek
particularly to test out the viability of a bow C-shock model for molecular
shocks, and to determine whether molecular hydrogen is the dominant coolant
in the lower (T < 1000K) gas downstream of the front.