Photo-processing Of Astro-PAHs

By Keith Cowing
Press Release
December 9, 2019
Filed under
Photo-processing Of Astro-PAHs
Schematic of the different relaxation processes of astro-PAHs upon VUV photon absorption and involved characteristic molecular timescales.

Polycyclic aromatic hydrocarbons (PAHs) are key species in astrophysical environments in which vacuum ultraviolet (VUV) photons are present, such as star-forming regions.

The interaction with these VUV photons governs the physical and chemical evolution of PAHs. Models show that only large species can survive. However, the actual molecular properties of large PAHs are poorly characterized and the ones included in models are only an extrapolation of the properties of small and medium-sized species.

We discuss here experiments performed on trapped ions including some at the SOLEIL VUV beam line DESIRS. We focus on the case of the large dicoronylene cation, C48H20+, and compare its behavior under VUV processing with that of smaller species. We suggest that C2H2 is not a relevant channel in the fragmentation of large PAHs. Ionization is found to largely dominate fragmentation. In addition, we report evidence for a hydrogen dissociation channel through excited electronic states.

Although this channel is minor, it is already effective below 13.6 eV and can significantly influence the stability of astro-PAHs. We emphasize that the competition between ionization and dissociation in large PAHs should be further evaluated for their use in astrophysical models.

Christine Joblin (IRAP), Gabi Wenzel (IRAP), Sarah Rodriguez Castillo (IRAP), Aude Simon (MAD), Hassan Sabbah (IRAP), Anthony Bonnamy (IRAP), Dominique Toublanc (IRAP), Giacomo Mulas (OAC), Mingchao Ji (IRAP), Alexandre Giuliani (CEPIA), Laurent Nahon (SSOLEIL)
(Submitted on 6 Dec 2019)
Subjects: Astrophysics of Galaxies (astro-ph.GA); Chemical Physics (physics.chem-ph)
Journal reference: Journal of Physics: Conference Series, IOP Publishing, In press
Cite as: arXiv:1912.03137 [astro-ph.GA] (or arXiv:1912.03137v1 [astro-ph.GA] for this version)
Submission history
From: Christine Joblin
[v1] Fri, 6 Dec 2019 14:16:26 UTC (719 KB)
Astrobiology, Astrochemistry

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