Spectra of ion irradiation experiments on initially pure ices of CO₂ (left panel) and CH₃OH (right panel). Both CO₂ and CH₃OH ices were irradiated at 45 K with 30 keV H⁺ during "thin film" experiments. The spectra of the initial ices are represented in black while the different irradiation steps are represented in shades of blue and green. The multiple bands present in the black initial spectra are all assigned to the unirradiated ice. Dashed grey lines assign molecules or bonds produced by irradiation to new absorptions. In the methanol experiments, the asterisk marks a band to which ethanol, acetone and ethylene glycol can contribute (Öberg et al. 2009b). Spectra from the CH₃OH experiments are presented with a Gaussian smoothing (σ = 10) to improve readability when spectra overlap, but calculations for band area and centre were performed on the raw spectra. For readability purposes, not all irradiation steps are shown.