Non-metal to metal transition of magnesia supported Au clusters affects the ultrafast dissociation dynamics of adsorbed CH3Br 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 CH3Br molecules adsorbed on variable size Au clusters on MgO/Mo(100) is investigated by monitoring the CH3+ transient evolution using a pump-probe technique in conjunction with surface mass spectrometry. Furthermore, extreme-ultraviolet photoemission spectroscopy in combination with theoretical calculations are employed to study the electronic structure of the Au cluster on MgO/Mo(100). Changes in the ultrafast dynamics of CH3+ 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.