Evidence for s–d Hybridization in Au38 Clusters

Resonant enhancement is seen in some gold clusters at the gold 4f 7/2 and 4f 5/2 threshold, indicative of an f to d transition. The existence of such resonance is generally not observed in ultrasmall Au nanoclusters because this resonant transition is forbidden in atomic gold, as gold represents a filled 5d 10 6s 1 system. Here we report, for the first time, the presence of a strong resonant enhancement in photoemission at the 4f 7/2 threshold and a weaker resonant enhancement at the 4f 5/2 threshold, in the open (undressed) Au 38 cluster system, indicating not only an f to d Coster–Kronig resonance but also s–d hybridization, much like what is observed in gold films. This f to d Coster–Kronig photoemission resonance is not observed in the “undressed” thiol-terminated gold clusters characteristic of far more localized orbitals. These results indicate that the unusual catalytic properties of ultrasmall gold nanoclusters such as Au 38 are not a result of localized orbitals, which is the case in a molecular system.