Evidence for s-d Hybridization in Au38 Clusters

Y. B. Losovyj, S.-C. Li, N. Lozova, K. Katsiev, D. Stellwagen, U. Diebold, L. Kong, C.S.S.R. Kumar

Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, Louisiana 70806, U.S.A.
Department of Physics, Tulane University, New Orleans, LA, 70118, U.S.A.
Department of Chemistry, Texas A&M University, College Station, Texas 77842, U.S.A.
Utrecht University, P.O. Box 80083, 3508 TC Utrecht, The Netherlands
Institut für Angewandte Physik, Technische Universität Wien, 1040 Wien, Austria
Nebraska Center for Materials and Nanoscience, Department of Physics and Astronomy, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0299, U.S.A.
Center for Atomic-level Catalyst Design (CALC-D), 110 Chemical Engineering, Baton Rouge, Louisiana 70803, U.S.A.

J. Phys. Chem. C 116 (2012) 5857-5861

Resonant enhancement is seen in some gold clusters at the gold 4f7/2 and 4f5/2 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 5d106s1 system. Here we report, for the first time, the presence of a strong resonant enhancement in photoemission at the 4f7/2 threshold and a weaker resonant enhancement at the 4f5/2 threshold, in the open (undressed) Au38 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 Au38 are not a result of localized orbitals, which is the case in a molecular system.

Corresponding author: Challa S.S.R. Kumar. Reprints also available from Ulrike Diebold (diebold at iap_tuwien_ac_at).

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