Interstellar triply deuterated ammonia

Research on interstellar ND3 is reviewed and updated from the discovery papers. Results from observations of a dozen sources at centimeter and submillimeter wavelengths are presented. The two data sets are consistent, but do not constrain the excitation conditions in the ND3-emitting gas. The column density ratios of NH3:NH2D, NH2D:ND2H and ND2H:ND3, observed in similar sized beams, are ~10, and present a challenge for both the gas-phase and the grain-surface chemistry scenarios of deuterium fractionation. The role of shocks and of CO depletion in deuterium chemistry is discussed.