Double bond equivalent (DBE) versus O/C (left panel) and N/C (right panel) measured in the organic refractory residues produced after ion bombardment and warm-up of H₂O:CH₃OH:NH₃ mixtures in the range 150–400 m/z. The DBE values estimated in positive and negative mode are indicated by “p” and “n”, respectively, while squares, circles and triangles give the average values. Grey arrows indicate the evolution of DBE with increasing irradiation dose. We estimate relative standard deviations of 2% for DBE, 12% for O/C, and 6% for N/C.