  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 557 GHz. To cover these
frequencies we used the Odin satellite to perform a spectral line survey in the
frequency ranges 486-492 GHz and 541-577 GHz, filling the gaps between previous
spectral scans. Odin's high main beam efficiency 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. The beam-averaged emission is dominated by CO,
H2O, SO2, SO, 13CO and CH3OH. Species with the largest number of lines are
CH3OH, (CH33)2O, SO2, 13CH3OH, CH3CN and NO. Six water lines are detected
including the ground state rotational transition 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)-1(1,1) transition of HDO. Other lines of special interest are the
1_0-0_0 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.
