Detection of Triply Deuterated Ammonia in the Barnard 1 Cloud

We report the detection of the ground-state rotational transition J K = 1 0 → 0 0 (0 a → 0 s ) of triply deuterated ammonia at 309.91 GHz in the Barnard 1 cloud, obtained with the Caltech Submillimeter Observatory. The observed, integrated, line intensity of 0.307 ± 0.019 K km s -1 implies an ND 3 column density of (2 ± 0.9) × 10 12 cm -2 , for excitation temperatures in the range 5-10 K. Using previously published H 2 and NH 3 column density estimates in this source, we derive an ND 3 fractional abundance with respect to H 2 of (1.5 ± 1) × 10 -11 and an ND 3 -to-NH 3 abundance ratio of ~8 × 10 -4 . The observed abundance ratios can be explained in the framework of gas-phase chemical models, in which the dissociative recombination of partially deuterated ions results in a somewhat higher probability for the ejection of hydrogen atoms than deuterium.