Abstract

The photodissociation of mass-selected benzene cluster ions, (C6H6)n+(n=28), is studied to elucidate the dynamics of dissociation and the mechanism of fragmentation. For (C6H6)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 (C6H6)n+ with n = 5-8, the average number of neutral molecules ejected following photoexcitation increases linearly with increasing hv until (C6H6)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.