Enhanced reactivity of oxygen-functionalised PAHs with atomic hydrogen - A route to the formation of small oxygen-carrying molecules

R. Jaganathan, F. D. S. Simonsen, J. D. Thrower, L. Hornekaer*

*Corresponding author af dette arbejde

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Abstract

Aims. We investigate the interaction of a linear, catacondensed polycyclic aromatic hydrocarbon (PAH), pentacene (C22H14), and its oxygen-functionalised form 6, 13 pentacenequinone (C22H12O2) with atomic hydrogen (H) under interstellar conditions. We compare their reaction cross-sections and reaction products to elucidate the possible role played by oxygen-functionalised PAHs in the formation of small oxygen-carrying molecules in the interstellar medium. Methods. We present temperature-programmed desorption measurements in combination with mass spectrometry. The evolution of the mass distribution of the desorbed species with increasing H-atom fluence and their peak desorption temperatures give insight into the reaction products. Results. The experiments reveal reaction cross-sections that are significantly larger for the oxygen-functionalised species compared to pentacene. For both pentacene and 6, 13 pentacenequinone, hydrogenated species with an even number of excess H-atoms dominate over hydrogenated species with an odd number of H-atoms. The end product, after exposure to large H-atom fluences, for both pentacene and PQ is fully superhydrogenated pentacene (C22H36), with little evidence for any remaining oxygen-containing species. This suggests the release of small molecules such as OH and/or H2O by the abstraction of oxygen atoms during hydrogenation, indicating that oxygen-functionalised PAHs can enable the formation of small oxygen-bearing molecules under interstellar conditions.

OriginalsprogEngelsk
ArtikelnummerA136
TidsskriftAstronomy & Astrophysics
Vol/bind663
Antal sider6
ISSN0004-6361
DOI
StatusUdgivet - jul. 2022

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