a) AKARI/IRC 2.5–5 μm and Spitzer/IRS 5–33 μm spectrum of ST6. The derived continuum is shown with dashed lines (green). Detected absorption bands of solids are labeled. b) Upper panel: optical depth spectrum of ST6 in the 8–10.5 μm region. The smooth solid line (brown) indicates the fitted profile of the silicate absorption band. Lower panel: residual spectrum after the subtraction of the silicate absorption band. Absorption bands of the NH₃ ice at 9.0 μm and CH₃OH ice at 9.75 μm are not seen in the spectrum.