Absorbance IR spectra of different mixtures as deposited at 15 K (continuum featureless black lines) and after having been irradiated by 30 keV ¹³C²⁺ ions (at two different ion fluences, red and blue lines). The continuum is due to the interference pattern of the IR beam that pass through the icy film. (Note the appearance of ¹²CO is due to ion bombardment of ¹²CO₂ that is present as a contaminant (not shown).)