The threshold collision-induced dissociation method is applied to study the fragmentation patterns and to measure the dissociation energies of small anionic copper clusters (Cun−, n=2–8) and their monocarbonyls (CunCO−, n=3–7). For the bare clusters, the main reaction channels are loss of an atom and loss of a dimer. For the copper cluster monocarbonyls, the main channel is loss of CO. Dissociation energies for the loss of an atom from bare copper cluster anions, D0(Cun−1−–Cu), show even–odd alternation. The species with the highest dissociation energy, Cu7−, and the highest carbonyl desorption energy, Cu5CO−, have eight valence electrons, consistent with closed shells in the jellium model. Bond energies are compared with theoretical models.

The energy-resolved collision-induced dissociation method is applied to measure the fragmentation patterns, cross sections, and dissociation energies of small anionic silver clusters (Agn−,n=2–11). The main reaction channels are found to be loss of atom and loss of dimer, with dimer loss favored for odd n values. The dissociation energies for the loss of atom, D0(Agn−1−–Ag), show strong even–odd alternation. Threshold models that account for collisional activation efficiency, kinetic shifts, and competitive shifts are employed to obtain dissociation energies. A critical examination of the models is performed using a thermochemical cycle comparing sequential atom loss with dimer loss.

The photodecomposition kinetics of silver cluster anions, Agn− (n=7–11), has been investigated. The time-resolved intensities of Agn− parent ions and Agn−1− and Agn−2− photofragment product ions are measured following 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 anions, including electron loss channels. Both prompt, direct electron photodetachment and delayed, statistical electron emission are observed in competition with cluster fragmentation product channels for some clusters. Dissociation threshold energies are determined by fitting the measured time profiles for fragmentation products using a statistical unimolecular dissociation model. The photodissociation lifetime method for measuring cluster dissociation energies is compared with previous energy-resolved collision-induced dissociation experiments on silver cluster anions.

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Articles you may be interested inStability of small Pd n ( n = 1 -7 ) clusters on the basis of structural and electronic properties: A density functional approach Measurement of the dissociation energies of anionic silver clusters ( Ag n − , n=2-11) by collision-induced dissociation J. Chem. Phys. 110, 5208 (1999); 10.1063/1.478416 Erratum: "Ligand and metal binding energies in platinum carbonyl cluster anions: Collision-induced dissociation of Pt m − and Pt m (CO) n " [J. Ligand and metal binding energies in platinum carbonyl cluster anions: Collision-induced dissociation of Pt m − and Pt m ( CO ) n − The bond dissociation energies of palladium trimer anion, Pd 3Ϫ , and its carbonyls, Pd 3 ͑CO͒ n Ϫ (n ϭ1 -6), are measured in the gas phase by the energy-resolved collision-induced dissociation method. The values obtained are D 0 (Pd 2 Ϫ ϪPd)ϭ2.26Ϯ0.36 eV for the bare cluster and D 0 (Pd 3 ͑CO͒ nϪ1Ϫ ϪCO)ϭ1.78Ϯ0.32 eV, 1.74Ϯ0.22 eV, 1.47Ϯ0.22 eV, 1.13Ϯ0.15 eV, 1.11 Ϯ0.15 eV, and 1.14Ϯ0.17 eV for nϭ1 -6, respectively, for the carbonyls. The results show a general decrease of the bond energy with an increasing number of carbonyls, with two relatively stable structures, Pd 3 ͑CO͒ 2 Ϫ and Pd 3 ͑CO͒ 6 Ϫ . A symmetric Pd 3 ͑CO͒ 2 Ϫ structure with two three-fold bridged carbonyls is postulated.