Superhydrogenated PAHs: Catalytic formation of H₂

¹ Department of Physics and Astronomy, Aarhus University, 8000 Aarhus C, Denmark
e-mail: liv@phys.au.dk
² Department of Theoretical Physics, Faculty of Natural Sciences, University of Paderborn, 33098 Paderborn, Germany

Abstract

The possible role of neutral PAHs as catalysts for H₂ formation in the interstellar medium is investigated by a combined experimental 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 reactions 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 cm² 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.