Synthetic spectra for end-member species, offset vertically for clarity. The range in band centers for Umbriel’s 2.14 μm, 2.2 μm, 2.22 μm, and 2.24 μm bands (Tables A2–A5) are highlighted by the purple, blue, green, and red zones, respectively. Putative features at shorter wavelengths in the Umbriel spectra are highlighted by pairs of dotted lines spanning 1.583–1.597, 1.622–1.637, and 1.691–1.731 μm (close-up view shown in Figure 6). The gray-toned zones show the wavelength regions with prominent telluric features that contaminate the Umbriel data. The end-member species shown are amorphous C, 7 μm grain diameter (1; Rouleau & Martin 1991), CO₂ ice (∼150 K), 10 μm grain diameter (2; Hansen 1997), H₂O ice (80 K), 20 μm grain diameter (3; Mastrapa et al. 2008), H₂O ice (80 K), 0.3 μm grain diameter (4; Mastrapa et al. 2008), kaolinite (room temperature), 7 μm grain diameter (5; Clark et al. 1990), amorphous NH₃ (40 K), 10 μm grain diameter (6; Roser et al. 2021), NH₃ ice (88 K), 10 μm grain diameter (7; Sill et al. 1980), NH₃ ice (100 K), 10 μm grain diameter (8; Hudson et al. 2022a), methylamine (110 K), 10 μm grain diameter (9; Hudson et al. 2022b), ethylamine (100 K), 10 μm grain diameter (10; Hudson et al. 2022b), propionitrile (95 K), 10 μm grain diameter (11; Moore et al. 2010), ethylene (60 K), 10 μm grain diameter (12; Hudson et al. 2014), propyne (80 K), 10 μm grain diameter (13; Hudson et al. 2021), and methanol (120 K), 10 μm grain diameter (14; Gerakines & Hudson 2020). The grain sizes for each end-member constituent matches the grain sizes included in the particulate mixtures (Figure 4 and Table 4).