Second harmonic generation spectroscopy experimental techniques

In addition to the indirect experimental evidence coming from work function measurements, information about water orientation at metal surfaces is beginning to emerge from recent applications of a number of in situ vibrational spectroscopic techniques. Infrared reflection-absorption spectroscopy, surface-enhanced Raman scattering, and second harmonic generation have been used to investigate the structure of water at different metal surfaces, but the pictures emerging from all these studies are not always consistent, partially because of surface modification and chemical adsorption, which complicate the analysis. 

Experimental study of the double layer is not limited to thermodynamics. A variety of spectroscopic methods have been applied to determine the structure and composition of the double layer. Two of these, namely, second-harmonic generation and vibrational sum frequency spectroscopy, have already been described in section 8.11. Other important techniques are based on the absorption of electromagnetic radiation when it is transmitted through or reflected at the interface. Finally, the scattering of X-rays and neutrons at interfaces has proven to be a valuable tool for obtaining atomic level information about the interface. In the following section some of these methods are outlined in more detail. 

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