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. 
Floris F.S. van der Tak, Dariusz C. Lis, Maryvonne Gerin, Evelyne   Roueff, Peter Schilke & Tom G. Phillips