In surface-aligned reactions (SARs), reagent species produced by the photolysis of aligned molecules adsorbed on crystalline solids tend to move in well-defined directions relative to the crystal surface. In this case, the degrees of freedom of surface chemical reactions are restricted, and therefore, the reaction dynamics and outcome are selected. In contrast to SARs, on amorphous surfaces, molecules can have various adsorption geometries, and therefore, their reaction dynamics is unforeseeable. Besides various adsorption geometries, metal clusters and nanoparticles present at the surface can influence the electronic structure and hence the molecular dynamics of the adsorbed molecules. In this work, as model systems, the ultrafast photoinduced reaction dynamics of methyl halide molecules such as CH3I and CH3Br adsorbed on amorphous oxide surfaces as well as variable-size metal clusters and nanoparticles supported on crystalline surfaces is investigated using an experimental technique that combines mass spectrometry with femtosecond pump-probe spectroscopy. The technique relies on the detection of highly unstable intermediate species and final products with time-, mass-, and energy resolution. The ultrafast reaction dynamics of the adsorbed molecules is correlated with the morphology and the electronic structure of the surface. This work provides a new avenue to a detailed understanding of how surface-photoinduced chemical reactions are influenced by the composition, morphology, and electronic structure of the surface.

Understanding the mechanisms of surface photoinduced reactions on amorphous surfaces and nanoparticles through the ultrafast detection of highly unstable intermediate species and final products

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