Comparison between absorption feature around 11 µm observed towards different sources with H₂O ice libration band from synthetic spectra. Panels a–c show in black the profiles for the highmass protostars Monoceros R2-IRS, AFGL 989, and the galactic centre source GCS3 II, respectively. The dashed red line is an asymmetric Gaussian fit of the 11.2 µm performed by Do-Duy et al. (2020). The solid green line is the profile of the H₂O ice libration band from a model assuming an ice mass of 15% distributed in porous ice and scaled to the peak optical depth at 11.6 µm, which is indicated by the vertical grey line.