Sum frequency studies of liquid interfaces

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Kenneth Eisenthal is supported by an award from the Chemical Structure, Dynamics and Mechanisms program in the Chemistry division to develop and apply second harmonic generation (SHG) and sum frequency generation (SFG) as methods to selectively probe interfaces of fundamental scientific interest. The PI and his research group focus on the interfaces of noble metal nanoparticles with the liquids in which they are suspended. The central question they ask is "how do noble metal nanoparticles affect the photophysical mechanisms by which molecules in excited electronic states, located at the nanoparticle/liquid interface, dissipate their energy"? Using femtosecond SFG and SHG they probe the ultrafast decay of interfacial molecules in excited electronic states. Because of the special optical and electronic properties of noble metal nanoparticles new channels for energy relaxation become important. SFG and SHG are sensitive to interfacial molecules only and are not sensitive and thus not overwhelmed by the much larger population of molecules in the bulk liquid. Using SFG and SHG, they measure the vibrational and electronic spectra of interfacial molecules in their ground, excited singlet, and triplet states. The molecules of interest are the aromatic carbonyls because of their special photophysical and photochemical properties.This research is of technological importance in developing methods and tools to probe the competing energy decay processes that directly impact the efficiency of solar cells, light emitting diodes, nano-electronics and nano-optics. These methods are relevant to a wide variety of fields, including emerging technologies in health care, electronics, nanotechnology and alternative energy.