We have carried out a high spectral resolution ( \lambda / \Delta \lambda \sim 6800 - 9700 ) line survey towards the Orion Kleinmann-Low ( KL ) cluster from 44–188 \mu m. The observations were taken with the Long Wavelength Spectrometer ( LWS ) in Fabry-Pérot mode , on board the Infrared Space Observatory ( ISO ) .
A total of 152 lines are clearly detected and a further 34 features are present as possible detections .
The spectrum is dominated by the molecular species H _ { 2 } O , OH and CO , along with [ O i ] and [ C ii ] lines from PDR or shocked gas and [ O iii ] , [ N iii ] lines from the foreground M42 H ii region .
Several isotopic species , as well as NH _ { 3 } , are also detected .
HDO and H _ { 3 } O ^ { + } are tentatively detected for the first time in the far-infrared range towards Orion-KL .
A basic analysis of the line observations is carried out , by comparing with previous measurements and published models and deriving rotational temperatures and column densities in the case of the molecular species .

Analysis of the [ O i ] and [ C ii ] fine structure lines indicates that although a shock model can reproduce the observed [ O i ] surface brightness levels , it falls short of the observed [ C ii ] level by more than a factor of 30 .
A PDR model can reproduce the [ O i ] 63.2 \mu m and [ C ii ] surface brightness levels within 35 % , although over-predicting the LWS [ O i ] 145.5 \mu m emission by a factor of 2.7 .
The 70 water lines and 22 OH lines detected by the survey appear with mainly P Cygni profiles at the shortest survey wavelengths and with mainly pure emission profiles at the longest survey wavelengths .
The emission and absorption velocity peaks of the water and OH lines indicate that they are associated with gas expanding in the outflow from the KL cluster .
The estimated column densities are ( 2-5 ) \times 10 ^ { 14 } cm ^ { -2 } for H _ { 2 } O and ( 2.5-5.1 ) \times 10 ^ { 16 } cm ^ { -2 } for OH .
The 26 detected CO lines confirm the presence of three distinct components , with temperature and column density combinations ranging from 660 K , 6 \times 10 ^ { 17 } cm ^ { -2 } to 360 K , 2 \times 10 ^ { 19 } cm ^ { -2 } .
Comparison of the surface brightnesses and integrated fluxes of the CO lines measured in the 80-arcsec LWS beam with those measured previously by the Kuiper Airborne Observatory ( KAO ) in a 44 arcsec beam shows similar surface brightnesses in the different beams for the lowest-J CO lines and similar integrated fluxes in the different beams for the highest-J CO lines , indicating that emission from the former lines has a uniform surface brightness within the LWS beam , while the latter lines originate from a region less than 44 arcsec in diameter .
The complexity of the region requires more sophisticated models for the interpretation of all the line observations .