THE 3.3 MICRON FEATURE, H-2, AND IONIZED-GAS IN THE ORION BAR

We present the results of spectroscopy of the 3.3 μm feature, H2 emission, Pα, and Brα, obtained along a line perpendicular to the Orion ionization front. The intensity of the 3.3 μm feature reaches a maximum between the ionization front and the H2 peak. The 3.3 μm spatial distribution appears to be due to destruction of the emitting material within the H H region and extinction of the exciting radiation between the edge of the H II region and the H2 peak, resulting in a maximum between the ionization front and the H2 peak. The H2 peak is consistent with either being due to a shock front or being due to UV-pumped fluorescence from dense clumps of H2. The width of the 3.3 μm feature observed at high spectral resolution is constant in regions of varying UV flux. We suggest that the strength of the UV field is not the cause of the variations in the 3.3 μm feature width observed in other sources, but rather that these variations are caused by a compositional change related to the age of the emitting material.