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.
| Original language | English |
|---|---|
| Article number | A136 |
| Journal | Astronomy & Astrophysics (A&A) |
| Volume | 663 |
| Number of pages | 6 |
| ISSN | 0004-6361 |
| DOIs | |
| Publication status | Published - Jul 2022 |
Keywords
- astrochemistry
- molecular processes
- methods
- laboratory
- molecular
- solid state
- ISM
- molecules
- POLYCYCLIC AROMATIC-HYDROCARBONS
- PENTACENE
- EMISSION
- SUPERHYDROGENATION
- IRRADIATION
- DISCOVERY
- SEQUENCE
- SPECTRUM