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Abstract

Vibrationally resonant sum frequency generation (VSFG) spectroscopy is a nonlinear optical technique capable of probing the vibrational response of molecules with interfacial specificity. Because it is all-optical and interface-specific, the technique is ideally suited to probe the electrode–electrolyte interface and can offer insight into interfacial speciation and molecular structure not possible using other means. Here we review the application of VSFG spectroscopy to characterize electrochemical systems. First we describe the background to the techniques, its differences from conventional vibrational spectroscopies, two possible experimental geometries for VSFG spectroelectrochemistry, and the expression that describes the measured VSFG intensity. Next two example systems are presented to demonstrate how application of VSFGS offers insight into electrochemical systems that is difficult to obtain with other experimental techniques: (i) the potential dependence of water structure at the gold electrode–aqueous solution interface and (ii) the reaction mechanism of formic acid electrooxidation on Pt(100).