Nonmetal-to-Metal Transition of Magnesia Supported Au Clusters Affects the Ultrafast Dissociation Dynamics of Adsorbed CH 3 Br Molecules.

The detection of intermediate species and the correlation of their ultrafast dynamics with the morphology and electronic structure of a surface is crucial to fully understand and control heterogeneous photoinduced and photocatalytic reactions. In this work, the ultrafast photodissociation dynamics of CH 3 Br molecules adsorbed on variable-size Au clusters on MgO/Mo(100) is investigated by monitoring the CH 3 + transient evolution using a pump-probe technique in conjunction with surface mass spectrometry. Furthermore, extreme-UV photoemission spectroscopy in combination with theoretical calculations is employed to study the electronic structure of the Au clusters on MgO/Mo(100). Changes in the ultrafast dynamics of the CH 3 + fragment are correlated with the electronic structure of Au as it evolves from monomers to small nonmetallic clusters to larger nanoparticles with a metallic character. This work provides a new avenue to a detailed understanding of how surface-photoinduced chemical reactions are influenced by the composition and electronic structure of the surface.