Stability of cationic silver doped gold clusters and the subshell-closed electronic configuration of AgAu14+

Silver doping is a valuable route to modulate the structural, electronic, and optical properties of gold clusters. We combine photofragmentation experiments with density functional theory calculations to investigate the relative stability of cationic Ag doped Au clusters, AgAuN-1+ (N <= 40). The mass spectra of the clusters after photofragmentation reveal marked drops in the intensity of AgAu8+, AgAu14+, and AgAu34+, indicating a higher relative stability of these sizes. This is confirmed by the calculated AgAuN-1+ (N <= 17) dissociation energies peaking for AgAu6+, AgAu8+, and AgAu14+. While the stability of AgAu6+ and AgAu8+ can be explained by the accepted electronic shell model for metal clusters, density of states analysis shows that the geometry plays an important role in the higher relative stability of AgAu14+. For this size, there is a degeneracy lifting of the 1D shell, which opens a relatively large HOMO-LUMO gap with a subshell-closed 1S(2)1P(4)1P(2)1D(6) electronic configuration.