BINDING-ENERGIES OF SMALL BENZENE CLUSTERS

Dissociation energies for monomer evaporation from neutral and ionized benzene dimer, trimer, tetramer and pentamer are experimentally determined from the measured ionization potentials and the appearance potentials of the respective decay channels of each of the cluster ions. The results strongly support a stable triangular structure for the neutral benzene trimer. By contrast a sandwich-like structure for the trimer ion is concluded. In the latter case the main contribution to the binding energy is from charge-transfer resonance interaction rather than from induction forces of a localized charge with the neutral molecule. This conclusion is supported by the good agreement between the measured relative dependence of the binding energy on the cluster size and the results of Huckel calculations assuming a sandwich structure and a delocalized charge.