2007A&A...476..807P

We investigate the physical and chemical conditions in a typical star forming region, including an unbiased search for new molecules in a spectral region previously unobserved. Due to its proximity, the Orion KL region offers a unique laboratory of molecular astrophysics in a chemically rich, massive star forming region. Several ground-based spectral line surveys have been made, but due to the absorption by water and oxygen, the terrestrial atmosphere is completely opaque at frequencies around 487 and 557GHz. To cover these frequencies we used the Odin satellite to perform a spectral line survey in the frequency ranges 486-492GHz and 541-577GHz, filling the gaps between previous spectral scans. Odin's high main beam efficiency, η_mb=0.9, and observations performed outside the atmosphere make our intensity scale very well determined. We observed 280 spectral lines from 38 molecules including isotopologues, and, in addition, 64 unidentified lines. A few U-lines have interesting frequency coincidences such as ND and the anion SH^–. The beam-averaged emission is dominated by CO, H₂O, SO₂, SO, ¹³CO and CH₃OH. Species with the largest number of lines are CH₃OH, (CH₃)₂O, SO₂, ¹³CH₃OH, CH₃CN and NO. Six water lines are detected including the ground state rotational transition 1_1,0-1_0,1 of o-H₂O, its isotopologues o-H₂¹⁸O and o-H₂¹⁷O, the Hot Core tracing p-H₂O transition 6_2,4-7_1,7, and the 2_0, 2_–11,1_ transition of HDO. Other lines of special interest are the 1₀-0₀ transition of NH₃ and its isotopologue ¹⁵NH₃. Isotopologue abundance ratios of D/H, ¹²C/¹³C, ³²S/³⁴S, ³⁴S/³³S, and ¹⁸O/¹⁷O are estimated. The temperatures, column densities and abundances in the various subregions are estimated, and we find very high gas-phase abundances of H₂O, NH₃, SO₂, SO, NO, and CH₃OH. A comparison with the ice inventory of ISO sheds new light on the origin of the abundant gas-phase molecules.