LDPI ReTOF-MS of the organic residue produced upon VUV irradiation of C₂H₂ ice at 15 K, exposed to further VUV fluence is shown. The fluence in the legend indicates the total photon fluence the formed residue was exposed to after the ice over a specific column was ablated, effectively halting the residue formation over that column. All the mass spectra were normalized to m/z=50, for comparison.