SHOCKED PURE-ROTATIONAL EMISSION FROM H-2 IN ORION

We present the results of observations of v = 0 J = 3-1, 4-2, 5-3, 9-7 , and 11-9 mid-infrared emission lines of H-2 originating in the shock -excited region that surrounds BN-KL in Orion. Our data consist of vel ocity-resolved spectra and line intensities obtained at the positions of the two strongest H-2 vibrational emission peaks. The profiles are single peaked, have line-center velocities very near that of the ambie nt molecular cloud (and consistent with emission from two lobes of a b ipolar outflow whose axis is very nearly in the plane of the sky), and have widths of approximately 30 and approximately 50 km s-1 (FWHM), r espectively, at the two locations. The emission in the line wings exte nds 50-100 km s-1 from line center. Our comparison of the wing emissio n of several lines argues against its originating from gas embedded wi thin the outflow lobes. A persuasive explanation of the high-velocity wing emission remains elusive, however. We discuss our results in ligh t of several shock models in the literature. The line intensities rang e from 10(-3) to 10(-2) ergs s-1 cm-2 sr-1 consistent with a two-shock model in which the low-J H-2 emission originates from molecules (with T approximately 500 K and N(H2) approximately 4 x 10(21) CM-2) reform ed after passage of a hydrodynamic shock and the high-J H-2 emission o riginates from molecules [with T approximately 2000 and N(H2) approxim ately 6 x 10(19) cm-2] in a magnetohydrodynamic shock. The thin dense shell of swept-up material separating the two shocks may be moving int o a clumpy medium whose density contrast is approximately 100 and whos e area-filling factor is approximately 0.2.