million years.

5.  ALMA represents the best candidate to perform future observations of and , not only in IRAS 16293-2422, but also in other sources where deuterated ammonia has been detected. More observations would enable to make a step towards a thorough understanding of ammonia formation and deuteration in the ISM.

This study was supported by Bologna University (RFO funds) and by MIUR (Project PRIN 2015: STARS in the CAOS, Grant Number 2015F59J3R). The work at SOLEIL was supported by the Programme National “Physique et Chimie du Milieu Interstellaire” (PCMI) of CNRS/INSU with INC/INP co-funded by CEA and CNES.

Energy levels scheme {#app:levels}
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Singly-deuterated amidogen radical
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The manifold of rotational energy levels is very complex in and its spectrum is characterized by many interactions. First, is a light asymmetric rotor far from the prolate limit ($\kappa=-0.66$) whose electric dipole moment lies in the $ab$ principal symmetry plane, with components $\mu_a = 0.67$D and $\mu_b = 1.69$D [@brown1979determination]. Because of the large values of the rotational constants, the room temperature spectrum is quite sparse and peaks in the far-infrared (FIR) region.

is an open-shell molecule with a $\tilde{X}\,^2A^{\prime\prime}$ ground electronic state. Due to the presence of an unpaired electron, 