for , the transitions detected in this work fall in spectral windows accessible either with the incoming band 1 of the 4GREAT receiver on board SOFIA (490–635GHz) or ALMA 10 Band (787–950GHz).

The conclusions of the present work can be summarized as follows:

1.  Thanks to the recently obtained laboratory data, two deuterated forms of amidogen radical, namely and , have been identified for the first time in the ISM. The analysis of hyperfine resolved transitions, observed in absorption against the continuum of the Class 0 protostar IRAS 16293-2422, allowed the accurate determination of column densities and excitation temperatures.

2.  The deuterium fractionation of amidogen results to be 70-100% for and 10–30% for . Our derived values differ significantly, being larger by about one order of magnitude, from those predicted by earlier astrochemical models.

3.  The low temperature and the high degree of deuteration observed suggest that amidogen, similarly to other nitrogen-containing species, is less depleted and subsists longer in the gas-phase, thus leading to high abundances of and .

4.  The amidogen D/H and spin-state abundance ratios in IRAS 16293-2422 cannot be reproduced with our gas-grain chemical model unless the pre-stellar stage lasts long, of the order of one 