Photodissociation Mechanisms of Benzene Cluster Ions on the Excitation With hv = 0.5-3.0 eV

The photodissociation of mass-selected benzene cluster ions,( C 6 H 6 ) n +( n = 2 − 8 ) , is studied to elucidate the dynamics of dissociation and the mechanism of fragmentation. For( C 6 H 6 ) 2 + , the average translational energy and the angular distributions of the photofragments are measured as a function of photon energy (hv). The photoexcitation to an upper bound state with hv = 2.81 eV results in statistical energy disposal. Regardless of the excitation to a dissociative state with hv = 1.17-1.62 eV, only a small fraction (at most 10%) of the available energy is partitioned into the translation. For( C 6 H 6 ) n +with n = 5-8, the average number of neutral molecules ejected following photoexcitation increases linearly with increasing hv until( C 6 H 6 ) 2 +is reached as the product. The result suggests that the photofragmentation proceeds via the sequential evaporation of neutral monomers rather than the direct ejection of a neutral cluster.