Isolation of the CH₃OCHO bands from the H₂CO band in the lab spectrum of the CH₃OCHO:CO:H₂CO:CH₃OH mixture. Top panel: H₂CO band at 6.67 μm (blue) isolated by tracing a local continuum (orange) to the observed spectrum (black); superposed gas-phase absorption lines of H₂O are not removed here. Bottom-left panel: lab spectra of pure H₂CO ice (blue) and the CH₃OCHO:CO:H₂CO:CH₃OH mixture (orange) manually scaled to the isolated H₂CO band at 6.67 μm in observations (black). Bottom-right panel: same as the middle panel but for a different wavelength range (7.9–8.5 μm).