PHOTODISSOCIATION DYNAMICS OF (C6H6)2+

Photodissociation of (C6H6)2+ is studied with photon energies between 1.29 and 2.81 eV. Mass-selected ion beam Of (C6H6)2+ is photodissociated by a pulsed laser beam in the field-free region of a reflectron-type time-of-flight mass spectrometer. The average relative translational energy, [epsilon(t)], and the angular distributions of the photofragments (C6H6+ and C6H6) are measured as a function of photon energy. With a photon energy of 2.81 eV, the (C6H6)2+ ions are promoted to a bound upper state correlated to C6H6+(pipi) + C6H6(X). Only a small fraction (almost-equal-to 3%) of the available energy is partitioned into the translational energy of the fragments and the product angular distribution is isotropic. Absorption of a photon in the range of 1.29-2.14 eV induces a charge resonance transition to a repulsive upper state which correlates to C6H6+(X) + C6H6(X). The observed values for [epsilon(t)] are at most 10% of the available energy, although the statistical phase space calculation shows that the complete randomization of the available energy is not achieved. As the photoexcited (C6H6)2+ moves apart on the dissociative potential surface, almost-equal-to 90% of the available energy flows into the intramolecular modes of the fragments. The energy partitioning becomes almost statistical regardless of the photoexcitation to a dissociative state.