Left panel: VUV absorbance spectrum (120−340 nm) of a frozen mixture O₂:N₂ = 1:1 as deposited at 22 K (dotted blue line) and after 1 keV electron irradiation at two different fluences (dashed black and solid red lines). Right panel: irradiated mixture is shown again (solid red line) on a different scale, along with the spectra obtained after annealing the ice to 50 K (dashed black line).