Comparison of the measured C₂H spectra (black histograms; see Sect. 2 and Fig. 1 for a description and for the identification of additional spectral features) and GASTRoNOoM model predictions under NLTE conditions for the case where (red) only the ground state is included, and (blue) the ground state, and the three vibrational modes are taken into account. These predictions are based on the “enhanced” abundance profile shown in Fig. 10 and the ¹Σ-approximation of C₂H. The transition N − (N − 1) and the ratio I_model/I_data are stated in the upper right corner of each panel, according to the colour code of the plots.