Normalised column densities of the N–H (a), C–H (b), and C=O (c) (filled blue circles) of crystalline NH₂CHO on CsI at 16 K with increasing UV photon fluence. The normalisation factor is the corresponding initial column densities. For the sake of simplicity, the evolution is compared with the best fit to the data (solid black line) presented for amorphous NH₂CHO on CsI at 12 K (Suhasaria & Mennella 2022). The two results tend to match if the first data point of the crystalline ice is subtracted and re-normalised (red triangles).