Comparison of observational and laboratory ice spectra. (a) Co-added CO₂ absorption profile across all pixels with detectable CO₂ (gray), with the smoothed profile after masking the H I line at 14.96 μm overplotted in black. Laboratory spectra: (b) CO:CO₂ (2:1) at 80 K (green); (c) H₂O:CH₃OH:CO₂ (0.8:0.9:1) at 125 K (blue); (d) pure CO₂ at 25 K (brown); (e) pure CO₂ on amorphous silicate spheres at 15 K (red); (f) H₂O:CO₂ (1:6) at 75 K (pink).