Local Electric Fields, Solvation, and Frustration at Interfaces Directly Probed by Vibrational Spectroscopy

It is widely understood that the molecular-scale structure and the corresponding local electric fields near an interfaces are crucial for controlling and optimizing interfacial processes. Yet, very little is known about the interface from direct spectroscopic observations. Most of our understanding, especially about local fields, is based on inferences from net transport data. We report advances in understanding interfaces using vibrational Stark shift probes at the surface and measured by Sum Frequency Generation Spectroscopy. We report three new developments. First, a new solvation model, as the interfacial analog of the bulk Onsager solvation theory, will be presented along with experimental support. Second, the extent of validity of the Guoy-Chapman-Stern (GCS) model and its variants as examined by Stark shift spectroscopy will be discussed. Our finding demands a new theoretical description of local fields under non-equilibrium conditions. Finally, we present result on the concept of Frustrated Lewis Acid-Base pairs (FLP) near the surface. We report creation of FLPs on metal surfaces and use vibrational spectroscopy to measure the extent of interfacial frustration. We argue that the above concepts will shed new light on the physics and chemistry of surfaces.