Delayed neutral-atom evaporation of photoexcited anionic gold clusters

The technique of time-resolved photodissociation in a Penning trap has been extended from cationic to anionic metal clusters. As a proof of principle the size-selected gold clusters Au14− and Au17− have been investigated. Superposed on the expected exponential decrease (increase) of the intensity of the precursor (product) cluster ion an oscillation of the yield is observed. This oscillation, which has not been noticed in the case of cations, is attributed to the magnetron motion of the ions in the trap. Reaction-rate constants for the monomer evaporation have been determined. The dissociation energies deduced from the Weisskopf rate equation are compared to extrapolations from model-free dissociation energies of positively charged gold clusters.