Chemistry Department Seminar

"Spectroscopy of mass-selected metal clusters: electronic structure controls reactivity"

Presented by Gerd Gantefor, University of Konstanz, Konstanz, Germany

Monday, April 10, 2006, 1:00 pm — Room 300, Bldg. 555

Clusters made of simple metals like Gold or Aluminum exhibit a dramatic size dependence in their chemical reactivities. For these extremely small particles, electronic structure determines reactivity: e.g., Aun- and Agn- clusters show a pronounced even-odd alternation of O2 uptake, which can be directly related to their electron affinity /1/. Such very small particles show promising catalytic properties /2/, too, which motivates our research to gain a better understanding of the chemical properties of metal clusters.

We study the dissociation dynamics of photoinduced reactions using time-resolved photoelectron spectroscopy. Absorption of a single photon results in the desorption of an O2 molecule from a metal cluster. This process of excitation and the subsequent dissociation is recorded by a sequence of photoelectron spectra.

A second approach aims towards the chemical properties of deposited clusters. So far, the pronounced even-odd alternation of the chemical properties of the coinage metals has not been found for clusters interacting with a substrate. We studied the oxidation of size-selected Aun clusters deposited on Silicon oxide and found a low reactivity for Au5 and high reactivities for Au4 and Au6. On this substrate some of the interesting properties of free clusters seem to still be present.

/1/ B. E. Salisbury, W. T. Wallace, R. L. Whetten, Chem. Phys. 262, 131 (2000)
/2/ A. Sanchez, S. Abbet, U. Heiz, W.-D. Schneider, H. Häkkinen, R. N. Barnett, and U. Landman,
J. Phys. Chem. A 103, 9573 (1999)

Hosted by: Jim Lighstone

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