  We present new observations of near-infrared molecular hydrogen (H2) line
emission in a sample of 18 Class I and flat-spectrum low mass protostars,
primarily in the Tau- Aur and {\rho} Oph dark clouds. The line emission is
extended by up to several arcseconds (several hundred AU) for most objects, and
there is little night-to-night variation in line strength coincident with the
continuum point source. Flux ratios of H2 v = 2 - 1 S(1) and v = 1 - 0 S(1)
lines are consistent with this emission arising in jets or winds in many
objects. However, most objects have only small offsets (under 10 km s-1)
between their H2 and photospheric radial velocities. No objects have line
ratios which are clearly caused solely by UV excitation, but the H2 emission of
several objects may be caused by UV or X-ray excitation in the presence of
circumstellar dust. There are several objects in the sample whose observed
velocities and line fluxes suggest quiescent, non-mechanical origins for their
molecular hydrogen emissions. Overall we find the H2 emission properties of
these protostars to be similar to the T Tauri stars studied in previous
surveys.
