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In search of the cause behind the similarities often seen in the fragmentation of PANHs, vacuum ultraviolet (VUV) photodissociation of two pairs of isomers quinoline–isoquinoline and 2-naphthylamine-3-methyl-quinoline are studied using the velocity map imaging technique. The internal energy dependence of all primary fragmentation channels is obtained for all four target molecules. The decay dynamics of the four molecules is studied by comparing their various experimental signatures. The dominant channel for the first pair of isomers is found to be hydrogen cyanide (HCN) neutral loss, while the second pair of isomers lose HCNH neutral as its dominant channel. Despite this difference in their primary decay products and the differences in the structures of the four targets, various similarities in their experimental signatures are found, which could be explained by isomerization mechanisms to common structures. The fundamental role of these isomerization in controlling different dissociative channels is explored via a detailed analysis of the experimental photoelectron–photoion coincidences and the investigation of the theoretical potential energy surface. These results add to the notion of a universal PANH fragmentation mechanism and suggests the seven member isomerization as a key candidate for this universal mechanism. The balance between isomerization, dissociation, and other key mechanistic processes in the reaction pathways, such as hydrogen migrations, is also highlighted for the four molecules. [ABSTRACT FROM AUTHOR]

A detailed exploration of the potential energy surface of quinoline cation (C9H7N·+) is carried out to extend the present understanding of its fragmentation mechanisms. Density functional theory calculations have been performed to explore new fragmentation schemes, giving special attention to previously unexplored pathways, such as isomerization and elimination of HNC. The isomerization mechanisms producing five- to seven-membered ring intermediates are described and are found to be a dominant channel both energetically and kinetically. Energetically competing pathways are established for the astrochemically important HNC-loss channel, which has hitherto never been considered in the context of the loss of a 27 amu fragment from the parent ions. Elimination of acetylene was also studied in great detail. Overall, the computational results are found to complement the experimental observations from the concurrently conducted PEPICO investigation. These could potentially open the doors for rich and interesting vacuum ultraviolet radiation-driven chemistry on planetary atmospheres, meteorites, and comets. [ABSTRACT FROM AUTHOR]