Decrease in the absorption area (integrated absorbance) of the CO ice band as a function of fluence for two different ice temperatures, 8 K and 15 K, see Sect. 3 for determination of the integrated absorbance. Data points and errorbars result from the average of two experiments performed under the same conditions. Roughly, 1 ML of ice is equivalent to a column density of 1 × 10¹⁵ molecules cm^-2.