SIZE AND EXCESS VIBRATIONAL-ENERGY DEPENDENCE OF EXCIMER FORMATION IN NAPHTHALENE CLUSTERS

Excited-state dynamics of small naphthalene clusters, following S1 <-- S0 excitation, has been investigated by the techniques of the resonant two-photon ionization, fluorescence excitation, and dispersed fluorescence. Highly resolved multiplet structures are obtained for the vibronic transitions of the trimer and tetramer, which provide information on the intermolecular interactions between the constituent molecules. Depending greatly upon its excess vibrational energy, each cluster exhibits broad and red-shifted bands in the dispersed fluorescence spectrum. This behavior is interpreted as evidence for the transformation of the initially excited van der Waals cluster into an excimer, which is formed by a pair of the monomers within the cluster framework. The restricted geometry of the van der Waals cluster is considered to explain the size and excess energy dependence of the excimer formation.