Photo-processing of astro-PAHs

Abstract

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.

References in corpus (12)

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• A general model for the identification of specific PAHs in the far-IR
• Photoinduced dynamics in protonated aromatic amino acid
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Cited by in corpus (9)

• Discovery of the 7-ring PAH Cyanocoronene (C${}_{24}$H${}_{11}$CN) in GOTHAM Observations of TMC-1
• Photodissociation of aliphatic PAH derivatives under relevant astrophysical conditions
• Contribution of polycyclic aromatic hydrocarbon ionization to neutral gas heating in galaxies: model versus observations
• Spinning nano-carbon grains: Viable origin for anomalous microwave emission
• The 3.3 $\mu$m Infrared Emission Feature: Observational and Laboratory Constraints on Its Carrier
• Infrared Spectroscopy of Pentagon-Containing PAHs: Indenyl and Fluorenyl Anions and Indenyl Cation
• Carbon accretion and desorption by interstellar polycyclic aromatic hydrocarbons
• Long-Lived Isomers of C${}_{11}$H${}_9^{+}$: New Experimental Insights from the PIRENEA Setup
• Acenaphthene Derivatives as Signatures of C${}_{11}$H${}_9^{+}$ Reactivity with Methylated Naphthalenes