AIRBORNE OBSERVATIONS OF THE 184 MICRON (H2O)-O-182(21)-]2(12) TRANSITION IN THE SHOCKED REGION OF ORION BN-IRC2

We report the first far-IR detection of isotopic water in the Orion BN -IRc2 region from aboard the Kuiper Airborne Observatory. The observat ion of the 183.5290 mu m H-2 O-18 2(21) --> 2(12) emission line indica tes that it is likely to originate from shocked gas in the outflow aro und Orion BN-IRc2, rather than from warm gas of the Orion plateau, whe re the H2O abundance is low ([H2O]/[H] less than or similar to 2.5 x 1 0(-5)). Our observation infers a ratio of [H2O]/[H] less than or simil ar to 1.7 x 10(-3), which indicates that O is efficiently converted to H2O in shocked gas.