Summary of dust and gas observations. The left panels show continuum-normalized dust strengths highlighting SiO₂, enstatite, and forsterite emission features. The middle panels present a close-up of the observed C₂H₂ features, highlighting four peaks corresponding to the main and rare isotopologues in red and blue, respectively. The right panels show the continuum-subtracted hydrocarbon-rich wavelength region of the spectra. The gray regions highlight the main Q branches of molecules in this wavelength region. HCN* and ${\mathrm{C}\mathrm{O}}_2^{\ast }$ indicate hot bands, ν₂: 1-0 and ν₁ ν₂ ν₃: 100-010 respectively. The spectra are ordered by increasing flux ratios of the ¹³CCH₂ and C₂H₂ peaks (see Sect. 4) and are normalized to a distance of 150 pc.