  The 2.46um v=1-0 R(5) line of deuterated molecular hydrogen, HD, has been
detected in the Orion Peak~1 shock emission region, at a surface brightness of
(8.5 +/- 2.1) x 10^(-9) W m^(-2)sr^(-1) over a 6 arcsec^2 area. Comparison of
the column density of HD(v=1,J=6) with the column density of HD(v=0,J=6)
previously observed from ISO and the H_2 level column densities toward the same
region implies that the excitation of HD is similar to that of H_2 for these
energy levels, despite much higher spontaneous transition rates for HD. We
suggest that this rough equality is caused by the coupling of the HD levels to
those of H_2, due to strong reactive collisions, HD + H -> H_2 + D, in warm,
partially dissociated gas. The deuterium abundance implied by the combined ISO
and UKIRT measurements toward Orion Peak 1 is [D]/[H] = (5.1 +/- 1.9)x10^(-6).
