CH₃CHO column density with respect to the initial methanol abundance ((CH₃OH)i, panels A and B) or during irradiation (CH₃OH, panel C). Estimates are based on the analysis of the 1350 cm⁻¹ band for CH₃CHO and on the 1025 cm⁻¹ band for CH₃OH. Panel A: estimates obtained after the subtraction of a linear baseline between 1360 and 1330 cm⁻¹ and integration of the 1350 cm⁻¹ band intensity. Panel B: estimates obtained from the integration of Gaussian curves centred at about 1350 cm⁻¹ obtained after a multi-Gaussian fit performed in the range 1500–1300 cm⁻¹. Panel C: CH₃CHO with respect to the amount of CH₃OH during irradiation. The ratio is calculated using the abundances of CH₃CHO obtained with the method of the integration from linear baseline.