Gas-phase hydrogenation processes of cationic carbon clusters

Abstract

ABSTRACT In this work, the gas-phase ion–atom collision reaction between large cationic carbon clusters and H-atoms is investigated. The carbon cluster cations (C$_{48-2*n}$$^+$, n = [0$-$8]) are produced from the photo-fragmentation processes of large PAH (dicoronylene, DC, C$_{48}$H$_{20}$) cations. The hydrogenated carbon cluster cations are efficiently formed (e.g. C$_{44/46}$H$_{9}$$^+$), and no even–odd hydrogenated mass patterns are observed. The hydrogenation behaviour and hydrogenation rate for these carbon cluster cations are the same. With theoretical calculations, the formation and bending processes of carbon cluster cations, the structure of these newly formed hydrogenated carbon cluster cations, and the bonding energies for the hydrogenation pathways are investigated. During the formation process of carbon clusters, the zigzagged edges gradually increase, and the planar configuration tends towards a bent and folded molecular configuration, i.e. from graphene to fullerene structures. The bending process with higher exothermic energies provides a reasonable explanation for the formation of the ‘magic numbers’ (e.g. C-atoms = 44) carbon clusters and their greater stability. The exothermic energy for each hydrogenation reaction pathway is relatively high; consequently, the forms and the hydrogenated states of carbon clusters are complex. The hydrogenation ability of edge carbon sites is higher than that of internal carbon sites; after bending and folding, the hydrogenation ability of these originally internal carbon sites becomes higher due to structural caged. As a result, under the co-evolution interstellar chemistry network, the (hydrogenation) states and forms of carbon compounds are complicated and diverse in the ISM.