Catalyzed routes to molecular hydrogen formation and hydrogen addition reactions on neutral polycyclic aromatic hydrocarbons under interstellar conditions

We present first-principle calculations which reveal the existence of low-barrier routes to molecular hydrogen formation on the polycyclic aromatic hydrocarbon (PAH) molecule coronene via Eley-Rideal abstraction reactions and show that such processes could indeed be active under interstellar conditions. The calculations indicate that in regions of low UV flux, coronene, and larger PAHs might be found in superhydrogenated states. Furthermore, the calculations imply that not only edge carbon atoms but also carbon atoms on the inner rings of the coronene molecule can be hydrogenated. Such superhydrogenated PAHs are expected to exhibit significantly changed absorption and emission spectra.