17 MU-M MOLECULAR-HYDROGEN LINE EMISSION FROM OMC-1

The v=0-0 S(1) line of molecular hydrogen at 17.03 mu m has been measu red in the source OMC-1 along a 90 '' cut passing through the near-IR H-2 emission Peaks 1 and 2 using the Kuiper Airborne Observatory. The line flux is typically 50% of the 2.12 mu m v=1-0 S(1) line, but its d istribution is somewhat more extended and it is relatively brighter at Peak 2. We interpret this as shocked emission coming from two regions of roughly equal brightness and lying close to the plane of the sky, plus a more extended contribution from slower shocks (similar to 5 km s(-1)) which do not contribute significantly to the near-IR vibrationa l-rotational lines. The 17 mu m line flux is an order of magnitude too strong to be explained by planar J- and C-shock models. However our d ata cannot distinguish between the merits of a cooling flow dominated by H-2 line emission and the integrated emission from a C-type bow-sho ck. Both models predict column density ratios close to those observed from a variety of lines covering a range from 1 000 to 25 000 K in upp er state energy. We predict a flux for the ground state 28.2 mu m 0-0 S(0) line of similar to 2% that of the 1-0 S(1) line at Peak 1, and su ggest that a consistent set of observations of the lowest pure rotatio nal lines of Hz would allow us to distinguish between these shock mode ls.