Upper panel: optical depth spectrum of ST6 in the 5.5–8 μm region. The smooth solid line (blue) indicates the expected spectrum of the 6.0 μm water ice band, whose strength is estimated based on the 3.05 μm band. Lower panel: spectrum after subtraction of the 6.0 μm water ice band. Absorption components that cannot be explained by the water ice are seen in the spectrum. Possible identifications of these absorption bands are indicated.