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The 1$_{11}$-1$_{01}$ lines of ortho and para--NH$_2$D (o/p-NH$_2$D),respectively at 86 and 110 GHz, are commonly observed to provide constraints onthe deuterium fractionation in the interstellar medium. In cold regions, thehyperfine structure due to the nitrogen ($^{14}$N) nucleus is resolved. Todate, this splitting is the only one which is taken into account in the NH$_2$Dcolumn density estimates. We investigate how the inclusion of the hyperfinesplitting caused by the deuterium (D) nucleus affects the analysis of therotational lines of NH$_2$D. We present 30m IRAM observations of the abovementioned lines, as well as APEX o/p-NH$_2$D observations of the1$_{01}$-0$_{00}$ lines at 333 GHz. The hyperfine spectra are first analyzedwith a line list that only includes the hyperfine splitting due to the $^{14}$Nnucleus. We find inconsistencies between the line widths of the1$_{01}$-0$_{00}$ and 1$_{11}$-1$_{01}$ lines, the latter being larger by afactor of $\sim$1.6$\pm0.3$. Such a large difference is unexpected given thetwo sets of lines are likely to originate from the same region. We next employa newly computed line list for the o/p-NH$_2$D transitions, where the hyperfinestructure induced by both nitrogen and deuterium nuclei is included. With thisnew line list, the analysis of the previous spectra leads to linewidths whichare compatible. Neglecting the hyperfine structure owing to D leads tooverestimate the linewidths of the o/p-NH$_2$D lines at 3 mm. The error for acold molecular core is about 50\%. This error propagates directly to the columndensity estimate. It is therefore recommended to take into account thehyperfine splittings caused by both the $^{14}$N and D nuclei in any analysisrelying on these lines.

The NH$_2$D hyperfine structure revealed by astrophysical observations