Observed spectra of NH (top) and ND (bottom) in grey histograms, with the LTE model as a red solid line. As the continuum is unreliable for NH, it has been subtracted from the spectrum. The LTE fit poorly reproduces the relative line ratios in ND. A schematic view of the hyperfine structure indicating the frequencies and relative intensities of the hyperfine components is shown at the bottom of each spectrum (blue).