Left panel: infrared spectra of H₂CO in water-dominated ice deposited at 13 K (a) and after 23 h of VUV photolysis (b) at 13 K. Right panel: the ν(C−O) stretching region has been enlarged for clarity. The infrared spectra recorded before and after photolysis at 13 K of H₂CO in water-dominated ice are compared with reference spectra recorded at 13 K of pure ethylene glycol (EG), methanol, and glycolaldehyde (GA).