ABSTRACT
This chapter presents and discusses the investigation of vibrational and electronic properties of the electrochemical interface by using nonlinear optical techniques of visible-infrared sum (SFG) and difference (DFG) frequency generation. We first introduce the theoretical approach that describes principles of SFG/DFG spectroscopy and of the calculations of second-order susceptibilities of the interface. The resonant susceptibility of the adsórbate is discussed, and the nonresonant contribution is correlated to the electronic properties of the substrate. In particular, the contributions of the intraband and interband electronic transitions are explicitly determined and compared with experimental results obtained on platinum, silver, and gold electrodes. We compare the SFG and DFG techniques and suggest to use both techniques for a better quantitative analysis of the experimental data. We then discuss the experimental requirements for SFG/DFG and experimental setup and procedures developed at the authors’ laboratory to study the electrochemical interface. Selected results that we cover are the vibrational behavior of H-Pt(hkl) system, both in the underpotential and over potential regime; adsorption of CN– on Au(hkl) electrode (using DFG); electrode surface electronic properties; and potential of zero charge measurements. Finally, the adsorption geometry of pyridine on Au(111) is studied by DFG in the 900- to 1150-cm–1 spectral range.
