Interaction of alkanes with metal surfaces: The mystery of the soft modes

COLL 354

Christof Wöll, Lehrstuhl für Physikalische Chemie I, Lehrstuhl für Physikalische Chemie I, Ruhr-Universität Bochum, Universitätsstr. 150, Bochum, 44797, Germany
At first sight the physisorption of alkanes on noble metal surfaces appears not to be a topic of pronounced scientific interest. A closer inspection of the electronic and vibrations properties of saturated hydrocarbons e.g. adsorbed on Cu-surfaces, however, reveals a number of surprising phenomena. The most notable is the occurrence of soft vibrational C-H stretching modes. Although this anomalous behaviour has been known for about three decades and despite the relevance for C-H activation on metal surfaces, one of the present hot topics in heterogeneous catalysis, a satisfying explanation is still lacking. Here we will present the results of a combined experimental and theoretical effort, where vibrational spectroscopy and x-ray absorption spectroscopy have been combined with precise ab-initio wave-function based quantum chemical calculations where correlation effects (e.g. van der Waals interactions) were considered on the MP2 level. On the basis of these results, we can put forward a consistent explanation of the effects leading to the soft modes.
 

Adamson Award Symposium Honoring Dave Allara and Ralph Nuzzo

Division of Colloid and Surface Chemistry
The 225th ACS National Meeting, New Orleans, LA, March 23-27, 2003