Effect of palladium doping on the stability and fragmentation patterns of cationic gold clusters

We analyze in detail how the interplay between electronic structure and cluster geometry determines the stability and the fragmentation channels of single Pd-doped cationic Au clusters, PdAuN-1+ (N=2-20). For this purpose, a combination of photofragmentation experiments and density functional theory calculations was employed. A remarkable agreement between the experiment and the calculations is obtained. Pd doping is found to modify the structure of the Au clusters, in particular altering the two-dimensional to three-dimensional transition size, with direct consequences on the stability of the clusters. Analysis of the electronic density of states of the clusters shows that depending on cluster size, Pd delocalizes one 4d electron, giving an enhanced stability to PdAu6+, or remains with all 4d10 electrons localized, closing an electronic shell in PdAu9+. Furthermore, it is observed that for most clusters, Au evaporation is the lowest-energy decay channel, although for some sizes Pd evaporation competes. In particular, PdAu7+ and PdAu9+ decay by Pd evaporation due to the high stability of the Au7+ and Au9+ fragmentation products.