  We present mid-infrared spectral maps of the NGC 1333 star forming region,
obtained with the the Infrared Spectrometer on board the Spitzer Space
Telescope. Eight pure H2 rotational lines, from S (0) to S (7), are detected
and mapped. The H2 emission appears to be associated with the warm gas shocked
by the multiple outflows present in the region. A comparison between the
observed intensities and the predictions of detailed shock models indicates
that the emission arises in both slow (12 - 24 km/s) and fast (36 - 53 km/s)
C-type shocks with an initial ortho-to-para ratio of ~ 1. The present H2
ortho-to-para ratio exhibits a large degree of spatial variations. In the
post-shocked gas, it is usually about 2, i.e. close to the equilibrium value (~
3). However, around at least two outflows, we observe a region with a much
lower (~ 0.5) ortho-to-para ratio. This region probably corresponds to gas
which has been heated-up recently by the passage of a shock front, but whose
ortho-to-para has not reached equilibrium yet. This, together with the low
initial ortho-to-para ratio needed to reproduce the observed emission, provide
strong evidence that H2 is mostly in para form in cold molecular clouds. The H2
lines are found to contribute to 25 - 50% of the total outflow luminosity, and
thus can be used to ascertain the importance of star formation feedback on the
natal cloud. From these lines, we determine the outflow mass loss rate and,
indirectly, the stellar infall rate, the outflow momentum and the kinetic
energy injected into the cloud over the embedded phase. The latter is found to
exceed the binding energy of individual cores, suggesting that outflows could
be the main mechanism for core disruption.
