Top panel: Observed spectrum and total model of the 14 μm region. Middle panel: Continuum-normalised spectrum and model absorption spectrum. The model includes C₂H₂, two HCN components, N₂H⁺, and CO₂. A fiducial model of HC₃N with N = 3×10¹⁵ cm⁻², T = 50 K is plotted as well. All components are shown with f_bg = 0.28, following the value inferred from C₂H₂ and HCN. The inset shows the model of the HCN Q branch in detail, illustrating that a 330 K component is needed to explain the asymmetric shape of the Q branch. Strong lines in the R and P branches of C₂H₂ and HCN are labelled for reference. Bottom panel: Residual spectrum. The grey shaded area indicates the 68% interval of the residuals.