HIFI observations of rotational transitions of ortho-NH₃ (left column) and para-NH₃ (middle and right columns) are shown by solid lines. Approximated line profiles (see Sect. 2.2) of two blended lines 3₀(s)−2₀(a) and 3₁(s)–2₁(a) are shown by dot-dashed lines. Emission profiles are overplotted with theoretical profiles (red dashed lines) from our best fit models computed separately for each ammonia spin isomer. The effect of line overlapping in case of the two blends is shown with blue dashed lines. The theoretical profiles for the three lines that were observed at phase φ= 0.13 (see Table 1) are rescaled up to mimic computations at phase φ= 0.23 (see Sect. 4.5 for details). Our approach in searching for the best fit is described in Sect. 4.5, and the best fitting parameters are compiled in Table 2.