Binding energies of the neutral and ionic clusters of naphthalene in their ground electronic states

The binding energies of the neutral and ionic clusters of naphthalene have been determined from the two-color two-photon measurements of the ionization potentials and appearance potentials. The measured binding energies (DO) of the neutral dimer is significantly smaller than the binding energies (D,) computed by correlated (MP2) quantum chemistry calculations. Interestingly, the experimental binding energy of the naphthalene dimer ion is very close to half the transition energy of its charge resonance absorption band, indicating that the dimer ion is stabilized mostly by charge resonance interactions. The slow increase in the dimer ion current with increasing photon energy, near the threshold of the excimer-mediated photoionization, suggests that the geometry of the dimer ion is significantly different from the sandwich-pair geometry of the excimer. Finally, the measured evaporation energies of the neutral tetramer, trimer ion, and tetramer ion support the trimer core structure of the neutral tetramer and the dimer core structure of the ionic clusters.