Fit CH₃CN, C₂H₅CN, and N₂O models on top of continuum-subtracted data (black). The models of the various mixtures of the ice are color-coded as follows: CH₃CN:H₂O:CO₂ (1:5:2, 50 K, red), CH₃CN:CO₂ (1:10, 15 K, blue), CH₃CN:CO (1:10, 80 K, purple), C₂H₅CN (orange, 50 K), and N₂O (70 K, cyan). The total fit is shown with the dashed green line. The 3σ uncertainty on optical depth is shown in shaded gray. Continuum identification of IRAS 16253 is uncertain, and thus the significance of the observed feature is unclear. The H₂ emission line is shown in gray and ignored when fitting (see also Fig. A.3).