Spectrum of the CH₃CN 3 mm and 2 mm detected lines at the HCO peak (i.e., the PDR position, top spectrum of each panel) and the DCO⁺ peak (i.e., inside the cold dense core, bottom spectrum of each panel), each spectrum towards the HCO peak has been shifted vertically by 0.2 K for clarity. The panel displays the K set of lines for a given ΔJ set of lines. The frequencies corresponding to each transitions are displayed as vertical bars, whose heights indicate their relative hyperfine intensities in the optically thin regime applicable to these observations. The best fit model is overplotted in red. The green horizontal lines display the ± 3σ significance levels.