Impurity Electron Localization in Early-Transition-Metal-Doped Gold Clusters

We have performed X-ray absorption spectroscopy of size-selected, free, cationic, transition-metal-doped (Sc, Ti, V, Cr) gold clusters in a size range n = 1–9. The electronic configuration of the impurity atom was determined by modeling the X-ray absorption spectrum in a charge-transfer multiplet framework which makes it possible to quantify the amount of localization of the impurity 3d states. Depending on the dopant element and the host cluster size we find a wide variety in the behavior of local electronic structures. ScAun+ clusters show strong hybridization of the scandium 3d states with the host electronic states except for ScAu1+ where we find a completely localized 3d electron. In TiAun+ clusters a pronounced odd–even alternation is present in the local electronic structure of the impurity atom. The 3d occupation number of the titanium dopant is approximately 2 and 1.6 electrons in odd and even-numbered clusters, respectively. In CrAun+ clusters the electronic structure of the dopant is governed b...