Deuterated ammonia in the Orion hot core.

The detection with the 100-m telescope of the 3_13,+ → 3_03,- (18.8 GHz) and 4_14,- → 4_04,+ (25.0 GHz) lines of NH₂D towards Orion-KL are reported. These data are combined with a partial map of the 1_11,- → 1_01,+ (110.15 GHz) line of this species using the IRAM 30-m telescope with a half-power beamwidth of 22arcsec. The presence of NH₂D in the Orion region is confirmed and the data suggest strongly that the observed lines form in the hot core region where temperatures exceed 100K. The authors derive an abundance ratio NH₂D/NH₃ of 0.003 which represents an enrichment relative to interstellar D/H of more than 100. It is concluded that the data are consistent with the idea that the ammonia seen in the Orion hot core has been freshly evaporated from grain surfaces.