Superhydrogenated PAHs: Catalytic Formation of H2

The possible role of neutral PAHs as catalysts for H2 forma- tion in the interstellar medium is investigated by a combined exper- imental and density function theory study of the superhydrogenation of coronene (C24H12). The calculations suggest efficient hydrogenation of both edge and centre sites, along with competing abstraction reac- tions to form H2 in a series of catalytic cycles. Scanning tunneling microscopy and thermal desorption measurements have been used to provide direct evidence of the formation of superhydrogenated coronene as a result of exposure to D atoms. Lower limit estimates for the cross- sections of 1.8×10 �17 ,5 .5×10 �18 and 1.1×10 �18 cm 2 for the formation of singly, doubly and triply hydrogenated coronene are derived. The results suggest that superhydrogenated PAHs may play an important role in H2 formation in the ISM.