Comparison of the 7 μm JWST MIRI spectrum of the disk d203-506 (top) with a simulation of ${\mathrm{C}\mathrm{H}}_3^{+}$ emission (bottom). The astronomical spectrum is a renewed extraction of the data presented in Berné et al. (2023), with the continuum and H₂ emission lines removed, but is otherwise not modified. The simulation is based on the accurate spectroscopic parameters given in Table 1 and calculated at a rotational temperature of T=700 K and FWHM=0.4 cm⁻¹. The zoom into the Q branch allows one to recognize a tiny shift in wavenumber between the calibrated laboratory data and the MIRI observation (see text for details). The shaded turquoise area marks the spectral range covered in the current laboratory measurements of Fig. 1.