The Fate of Dicationic States in Molecular Clusters of Benzene and Related Compounds

Calculations employing density functional theory indicate that, rather than undergoing fragmentation, dicationic clusters of benzene, hexafluorobenzene, and naphthalene produced by sequential one-electron or sudden double-ionization experiments on the neutrals can relax via the formation of inter-ring covalent C-C bonds, along with a series of proton transfers that enable a substantial reduction of inter- and intramolecular Coulomb repulsions. The theoretically predicted chemically bound structures correspond to deep local energy minima on the potential energy surface pertaining to the lowest electronic state of the dications and can therefore be regarded as metastable (kinetically long-lived) species. This discovery invalidates on theoretical grounds the liquid-droplet model of multiply charged clusters and sheds very unexpected light on possible consequences in chemistry of the intermolecular Coulombic decay (ICD) mechanism [Cederbaum, L. S.; et al. Phys. Rev. Lett. 1997, 79, 4778; Jahnke, T.; et al. Phys. Rev. Lett. 2004, 93, 163401] for deep inner-valence ionized states. Propagation of charge rearrangement reactions and proton transfers to several monomers may eventually lead to the formation of rather extended dicationic assemblies.