Mid-IR spectrum of a 23.4 ML crystalline NH₂CHO film on CsI at 16 K (blue line) and after irradiation with UV fluences of 1.9 × 10¹⁷ photons cm⁻² (black line) and 3.7 × 10¹⁸ photons cm⁻² (red line), respectively. The crystalline ice is rapidly transformed to the amorphous form after just the first irradiation step, as is seen from the black line. The spectrum of a 29.5 ML amorphous NH₂CHO film on a blank CsI substrate after a fluence of 3.7 × 10¹⁸ photons cm⁻² (green line) is also shown for comparison (Suhasaria & Mennella 2022). The black curve is offset in ordinate by −0.01 for the sake of clarity.