title: LABORATORY PHOTO-CHEMISTRY OF PAHS: IONIZATION VERSUS FRAGMENTATION.
abstract: Interstellar Polycyclic Aromatic Hydrocarbons (PAH) are expected to be strongly processed by Vacuum Ultra-Violet (VUV) photons. Here, we report experimental studies on the ionization and fragmentation of coronene (C24H12), ovalene (C32H14) and hexa-peri-hexabenzocoronene (HBC; C42H18) cations by exposure to synchrotron radiation in the range of 8-40 eV. The results show that for small PAH cations such as coronene, fragmentation (H-loss) is more important than ionization. However, as the size increases, ionization becomes more and more important and for the HBC cation, ionization dominates. These results are discussed and it is concluded that, for large PAHs, fragmentation only becomes important when the photon energy has reached the highest ionization potential accessible. This implies that PAHs are even more photo-stable than previously thought. The implications of this experimental study for the photo-chemical evolution of PAHs in the interstellar medium (ISM) are briefly discussed.
authors.affiliation: Leiden Observatory, University of Leiden, P.O. Box 9513, 2300 RA Leiden, The Netherlands ; Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden, P.O. Box 9513, 2300 RA Leiden, The Netherlands ; Universitè de Toulouse, UPS-OMP, IRAP, Toulouse, France ; CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028, Toulouse Cedex 4, France.
authors.forename: Junfeng
authors.initials: J
authors.lastname: Zhen
authors.affiliation: Leiden Observatory, University of Leiden, P.O. Box 9513, 2300 RA Leiden, The Netherlands ; Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden, P.O. Box 9513, 2300 RA Leiden, The Netherlands.
authors.forename: Pablo
authors.initials: P
authors.lastname: Castellanos
authors.affiliation: Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden, P.O. Box 9513, 2300 RA Leiden, The Netherlands.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Paardekooper
authors.affiliation: Leiden Observatory, University of Leiden, P.O. Box 9513, 2300 RA Leiden, The Netherlands ; Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden, P.O. Box 9513, 2300 RA Leiden, The Netherlands.
authors.forename: Niels
authors.initials: N
authors.lastname: Ligterink
authors.affiliation: Sackler Laboratory for Astrophysics, Leiden Observatory, University of Leiden, P.O. Box 9513, 2300 RA Leiden, The Netherlands.
authors.forename: Harold
authors.initials: H
authors.lastname: Linnartz
authors.affiliation: Synchrotron SOLEIL, L'Orme des Merisiers, 91192 Gif sur Yvette Cedex, France.
authors.forename: Laurent
authors.initials: L
authors.lastname: Nahon
authors.affiliation: Universitè de Toulouse, UPS-OMP, IRAP, Toulouse, France ; CNRS, IRAP, 9 Av. colonel Roche, BP 44346, 31028, Toulouse Cedex 4, France.
authors.forename: Christine
authors.initials: C
authors.lastname: Joblin
authors.affiliation: Leiden Observatory, University of Leiden, P.O. Box 9513, 2300 RA Leiden, The Netherlands.
authors.forename: Alexander G G M
authors.initials: AG
authors.lastname: Tielens
keywords: ISM: molecules; astrochemistry; methods: laboratory; molecular processes; ultraviolet: ISM