Photon polarization modulation infrared

Chronocoulometry and photon polarization modulation infrared reflec-tion/absorption spectroscopy have been employed [311] to study the fusion of dimyristoylphosphatidylcholine vesicles onto an Au(lll) electrode. The fusion was controlled either by the electrode potential, or charge. Film characteristics was also potential dependent. After removing the film from the electrode surface (negative potential), phospholipid molecules remained in its close proximity, in the ad-vesicle state. Several electrochemical and nonelec-trochemical methods have been applied [312, 313] to investigate the spreading of small unilamellar vesicles onto Au(lll) electrode. Vesicles fused onto the surface at > —0.5 V (versus SSCE), to form defected bilayers in contact with the metal surface. At more negative potentials, the film was removed from the electrode surface, but it still remained in its close proximity. 

That is, the properties of liquid/solid or gas/Uquid interfaces cannot be investigated properly with XPS. On the other hand, in case of using photon-in and photon-out techniques, e.g., sum frequency generation (SFG) spectroscopy [15] or polarization modulation infrared reflection-absorption spectroscopy (PM-IRAS) [16, 17], it is possible to look into various surfaces and interfaces under elevated pressure condition or even reaction conditions, including liquid/solid interface. However, the interpretation of its result is often not straightforward, and it often requires the advanced understanding to extract information, e.g., the difficulty in quantitative analysis. 

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