(, , and ) is well-represented, given that all the deuterated forms of ammonia (, , and ) and the imidogen radical [@bacmann2010first; @bacmann2016stratified] have been detected so far. However, deuterium enrichment has never been observed for the amidogen radical , neither in IRAS 16293-2422 nor in any other astronomical sources.

Several factors may be imputed to the current lack of observation of interstellar and . Until recently, laboratory data were limited to the frequency region below 500GHz [@kanada1991microwave; @kobayashi1997microwave]. At low temperatures, neither species possess any bright transitions in this portion of the spectrum, with $b$-type fundamental transitions lying high into the submillimeter-wave domain (around 770GHz for and around 527GHz for ). Furthermore, the amidogen radical is a textbook floppy molecule, for which frequency extrapolation from low frequency measurements is extremely unreliable. Besides the deficiency of laboratory spectral data, ground-based astronomical observations of these light species are hindered by the atmosphere opacity at submillimeter-wavelength. Therefore, even with high-frequency facilities (such as ALMA or SOFIA), the observation of light hydrides remains a challenging task. On-board observations using the *Herschel Space Observatory* mission, during which numerous projects attempted at gaining more insights into the chemistry of the ISM, offer a unique 