Notes. Summary of the nitrogen containing species observed at the IRAM telescope (except for the NH₃ isotopologues that were observed at the Green Bank Telescope). The NH₃ and NH₂D isotopologue observations are respectively taken from Lis et al. (2010) and Gérin et al. (2009). All the observations were obtained at a single position except for N₂H⁺J = 1 − 0 and NH₂D, for which we obtained maps. For each line, we indicate the central frequency of the line (ν₀) as well as the quantum numbers of the corresponding transition. The HPBW and efficiency (η) of the telescope at this frequency and the spectral resolution (δv) of the observations are also indicated. The last two columns indicate the averaged excitation temperature and the opacity of the rotational lines (summed over the hyperfine components), as derived from the results of the radiative transfer modelling. The upper/lower subscripts for indicate the highest/lowest excitation temperatures found when considering all the hyperfine components. These quantities are zero when all the hyperfine components are described by the same excitation temperature. In the case of the DNC isotopologues, we neglected the hyperfine structure and the subscripts are thus absent.