Band profiles comparison. The integrated NIRSpec spectrum from the north lobe of Tau 042021, in a sub-region unaffected by NIRSpec IFU masking to fully sample the profile, is shown in red (multiplied by 1.2). It is compared to a typical dense cloud spectrum (NIRCam + NIRSpec IFU, black, flux (multiplied by two) observed at high extinction in Chamaeleon I (McClure et al. 2023). Note the inversion in the shape for the CO₂ ice band profile around 4.27 μm betraying differences in radiative transfer properties. A laboratory transmittance spectrum (blue) of a H₂O:CO₂ ice film mixture used in the optical constants determination in Dartois et al. (2024) has been converted to flux scale for comparison. Spectra have been scaled to have similar optical depths in the ice absorption features in order to compare their profiles.