H₂ 0–0 S(9) continuum subtracted map at 4.69 μm (Zannese & Sidhu in prep). The green boxes are the aperture used to extract the spectra. (Left) CH⁺ v = 1–0 P(5) line at 3.86 μm. (Right) ${\mathrm{C}\mathrm{H}}_3^{+}$ emission from the Q branch around 7.15 μm. The solid red graphs are LTE models adapted to the observations (see Sect. 5.1 and Figs. E.1 and E.2). The gray filling represents 1% of the continuum. This shows that CH⁺ and ${\mathrm{C}\mathrm{H}}_3^{+}$ are detected where H₂ is bright and not where H₂ is faint.