Left: TPD mass spectra obtained after 360 min of codeposition of C₂H₂ + O₂ + H (exp. 3) and C₂H₂ + ¹⁸O₂ + H (exp. 4) at 10 K. The applied deposition ratio of C₂H₂:⁽¹⁸⁾O₂ :H was 1:10:40, and the used H-atom flux was 1.2 × 10¹³ atoms cm⁻² s⁻¹. Only relevant m/z channels are shown and shifted for clarity. The dashed line indicatesthe peak position of the corresponding COMs. Right: comparison of the ionization fragmentation pattern for the QMS peak at 177 K (black) with data of CH₃COOH in NIST (red). The position of the dashed arrows present for the isotope mass signal shifts in exp. 4.