title: Facile pentagon formation in the dissociation of polyaromatics.
abstract: Energetic processing of gaseous polycyclic aromatic hydrocarbons (PAHs) plays a pivotal role in the chemistries of inter- and circumstellar environments, certain planetary atmospheres, and also in the chemistry of combustion and soot formation. Although the precursor PAH species have been extensively characterized, the products from these gaseous breakdown reactions have received far less attention. It has been particularly challenging to accurately determine their molecular structure in gas-phase experiments, where comparisons against theoretical modeling are best made. Here we report on a combined experimental and theoretical study of the dissociative ionization of two nitrogen containing polycyclic aromatic hydrocarbons of C13H9N composition, acridine and phenanthridine. The structures of HCN-loss fragments are resolved by infrared multiple-photon dissociation (IRMPD) spectroscopy of the mass-isolated products in an ion trap mass spectrometer. Quantum-chemical computations as well as reference IRMPD spectra are employed to unambiguously identify the molecular structures. Furthermore, computations at the density functional level of theory provide insight into chemical pathways leading to the observed products. Acenaphthylene˙+and benzopentalene˙+- two aromatic species containing pentagons - are identified as the main products, suggesting that such species are easily formed and may be abundant in regions where thermal or photoprocessing of polyaromatics occurs.
authors.affiliation: Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525ED Nijmegen, The Netherlands. bouwman@strw.leidenuniv.nl.
authors.forename: Arjen J
authors.initials: AJ
authors.lastname: de Haas
authors.affiliation: Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525ED Nijmegen, The Netherlands. bouwman@strw.leidenuniv.nl and van't Hoff Institute for Molecular Sciences, University of Amsterdam, Science Park 904, 1098XH, Amsterdam, The Netherlands.
authors.forename: Jos
authors.initials: J
authors.lastname: Oomens
authors.affiliation: Radboud University, Institute for Molecules and Materials, FELIX Laboratory, Toernooiveld 7c, 6525ED Nijmegen, The Netherlands. bouwman@strw.leidenuniv.nl.
authors.forename: Jordy
authors.identifier: http://orcid.org/0000-0002-3615-1703
authors.initials: J
authors.lastname: Bouwman