A distinctive feature appears in the strong-field induced mass spectra of substituted benzenes and PAHs, that is not observed in analogous XUV-induced mass spectra. This feature is a set of peaks at 12 ≤ m/z ≤ 16 with the main signal appearing at m/z = 12. This peak can either correspond to C + or to C 2+ 2 (see Figures and). On the one hand, if this fragment is mainly C 2+ 2 , this would strongly indicate a preferred acetylene loss mechanism for PAH fragmentation, i.e., the PAH backbone breaks up into smaller chunks by losing C 2 H q+ x (q = 0, 1, 2) fragments. Such preference was observed in the XUV-induced fragmentation patterns (Figure ), which can be related to the hydrogen abstraction acetylene addition (HACA) mechanism of PAH formation, that can be important due to the presence of the C 2 molecule in space, for instance in comets. On the other hand, if the m/z = 12 peak corresponds to C + , that could indicate a highenergy stochastic fragmentation of the backbone.