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The Caltech Submillimeter Observatory has detected triply deuterated ammonia,ND3, through its 10a-00s transition near 310 GHz. Emission is found in the NGC1333 region, both towards IRAS 4A and a position to the South-East where DCO+peaks. In both cases, the hyperfine ratio indicates that the emission isoptically thin. Column densities of ND3 are 3--6 x 10^11 cm^-2 for T_ex=10 Kand twice as high for T_ex=5 K. Using a Monte Carlo radiative transfer code anda model of the structure of the IRAS source with temperature and densitygradients, the estimated ND3 abundance is 3.2 x 10^-12 if ND3/H2 is constantthroughout the envelope. In the more likely case that ND3/H2D+ is constant,ND3/H2 peaks in the cold outer parts of the source at a value of 1.0 x 10^-11.To reproduce the observed NH3/ND3 abundance ratio of ~1000, grain surfacechemistry requires an atomic D/H ratio of ~0.15 in the gas phase, >10 timeshigher than in recent chemical models. More likely, the deuteration of NH3occurs by ion-molecule reactions in the gas phase, in which case the dataindicate that deuteron transfer reactions are much faster than protontransfers.Comment: 4 pages, 2 figures; to be published in Astronomy & Astrophysics  (Letters

Triply deuterated ammonia in NGC 1333