Competitive fragmentation and electron loss kinetics of photoactivated silver cluster anions: Dissociation energies of Ag-n(-) (n=7-11)

The photodecomposition kinetics of silver cluster anions, Ag-n(-) (n=7-11), has been investigated. The time-resolved intensities of Ag-n(-) parent ion s and Ag-n-1(-) and Ag-n-2(-) photofragment product ions are measured follo wing excitation with visible laser radiation, 415-750 nm. The atom-loss and dimer-loss product yields and reactant cluster ion depletion are compared to elucidate the decomposition kinetics of photoexcited silver cluster anio ns, including electron loss channels. Both prompt, direct electron photodet achment and delayed, statistical electron emission are observed in competit ion with cluster fragmentation product channels for some clusters. Dissocia tion threshold energies are determined by fitting the measured time profile s for fragmentation products using a statistical unimolecular dissociation model. The photodissociation lifetime method for measuring cluster dissocia tion energies is compared with previous energy-resolved collision-induced d issociation experiments on silver cluster anions. (C) 1999 American Institu te of Physics. [S0021-9606(99)00227-5].