Astronomy and Astrophysics – Astronomy
Scientific paper
May 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011iaus..280p.118c&link_type=abstract
The Molecular Universe, Posters from the proceedings of the 280th Symposium of the International Astronomical Union held in Tole
Astronomy and Astrophysics
Astronomy
Scientific paper
The interaction between thin films of polycyclic aromatic hydrocarbons (PAHs) and atomic H has been studied using scanning tunneling microscopy (STM). Observational evidence suggests that hydrogenated PAHs are located in regions of the interstellar medium (ISM) where there are high concentrations of molecular hydrogen (H2)1. It has previously been postulated that hydrogenated PAHs act as catalysts for the formation of H22. While many studies have focused on the role of ionic PAHs in the formation of H23, here we consider the role of neutral species. Neutral PAHs are expected to be stable and to condense on grain surfaces present in dense interstellar clouds, in regions of low UV flux4. PAH molecules were deposited in thin films under ultra high vacuum (UHV) conditions. Monolayer films were subsequently characterised using STM, at liquid N2 temperatures. The films were then exposed to thermally-cracked atomic H and were again characterised using STM. Contrast in the STM images showed submolecular changes to the electronic structure of the PAH molecules only after exposure to atomic H. This suggests the formation of superhydrogenated species. DFT calculations have predicted that such superhydrogenated species are stable and can act as catalysts for the formation of H2 through abstraction reactions5. Complimentary thermal desorption experiments support these findings.
Balog R.
Cassidy A. M.
Hornekaer Liv
Jøorgensen B. B.
Nilsson Lisa
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