Fragmentation of the PAH cations of Isoviolanthrene and Dicoronylene: A case made for interstellar cyclo[n]carbons as products of universal fragmentation processes

Abstract

The photo-induced fragmentation pathways of the cationic forms of isoviolanthrene (C34H18) and dicoronylene (C48H20) are systematically studied with mass spectrometry employing an ion trap coupled with a laser system. The mass spectra of these structurally different species display similar fragmentation products, akin to previous work on three dibenzopyrene isomers, but also display some differences. The products formed in the largest yields are pure carbon clusters, which are likely in the form of ionized cyclo[n]carbons (n = 11–15). These findings are relevant to get a full picture of the molecular makeup of interstellar space, particularly in heavily irradiated regions where polycyclic aromatic hydrocarbon (PAH) molecules are omnipresent and subject to harsh irradiation and are broken down into smaller components. These interstellar species are expected to include the PAH derivatives observed here, but which are not identified in space yet.