IR spectra of pure CH₃CHO ice (a), subsequent hydrogenation of predeposited ice with a H-atom flux of 1.2 × 10¹³ atoms cm⁻² s⁻¹ for 30 min at 10 K (b), RAIR difference spectrum obtained after hydrogenation of CH₃CHO ice (c), and reference spectrum of CH₃CHO ice (d). The dashed lines and arrows are shown for the vibrational peaks of the studied molecules. IR spectra are offset for clarity.