Short-Range Catalyst-Surface Interactions Revealed by Heterodyne Two-Dimensional Sum Frequency Generation Spectroscopy.

Heterodyne 2D sum frequency generation spectroscopy is used to study a model CO2 reduction catalyst, Re(diCN-bpy) (CO)3Cl, as a monolayer on a gold surface. We show that short-range interactions with the surface can cause substantial line-shape differences between vibrational bands from the same molecules. We explain this interaction as the result of couplings between CO vibrational modes of the catalyst molecules and the image dipoles on gold surface, which are sensitive to the relative distance between the molecule and the surface.