Multiplex Electronic Sum Frequency Generation Spectroscopy of Dye Molecules at the Air/Water Interface

Abstract

This chapter describes multiplex electronic sum frequency generation spectroscopy and its application to the studies of static and dynamic properties of dye molecules adsorbed at the air–water interface. Second-order nonlinear spectroscopy is a powerful tool to study the structure and dynamics of molecules at interfaces that are very important in fundamental science and industrial application. Vibrational spectra of interfacial molecules are measured by IR-visible sum frequency generation (SFG) spectroscopy. The sensitivity of the IR-vis SFG spectroscopy has improved by using broadband IR pulses and multichannel detectors. High-quality IR-vis SFG spectra can be measured nowadays. On the other hand, second-order nonlinear susceptibility data of interfacial molecules are measured by the resonance second harmonic generation (SHG) method. In the spectral measurements, the SHG light intensity is recorded point by point with scanning the fundamental excitation wavelength. It is difficult to measure high-quality electronic spectra of interfacial molecules by the conventional scanning method.