Polycyclic Aromatic Hydrocarbons as a Source for ${CH}_N^{+}$ (N = 4–6) and C₃H₂ in the Interstellar Medium

Photoionization and dissociation of anthracene, phenanthrene, and pentacene in the multiphoton regime at 266 nm wavelength were performed. ${CH}_n^{+}$ (n = 4–6) ions were observed as fragments, and their yields as a function of laser intensity were studied. H-migration and "roaming" mechanisms leading to the formation of these fluxional ions from polycyclic aromatic hydrocarbons (PAHs) are proposed. The present results show higher photostability of PAHs with bent structure and suggest PAHs in the UV regions of interstellar medium as a prominent source for ${CH}_n^{+}$ (n = 4–6).