Far-ultraviolet spectroscopy of solid and liquid states: characteristics, instrumentation, and applications.

Recently, far-ultraviolet (FUV) spectroscopy, which is the spectroscopy of wavelengths in the region 140-200 nm, of solid and liquid states has received significant attention as a novel spectroscopic method. FUV spectroscopy provides new possibilities for studying electronic structures and transitions in almost all types of molecules, from water to polymers. It also shows great promise for a variety of applications. It is well known that wavelengths below 200 nm are rich in information regarding the electronic structure and states of molecules. However, absorptivity is so high in the FUV region, that it has not been employed to investigate solids and liquids. Another problem for FUV region analysis was the instrumentation: FUV spectrometers required vacuum evacuation. Moreover, it was difficult to find applications for FUV spectroscopy. Recently, we introduced the attenuated total reflection (ATR) technique to FUV spectroscopy, which overcomes these issues. ATR-FUV spectroscopy enables the measurement of FUV spectra for solid and liquid samples, establishing a new spectroscopic research area. Using ATR-FUV spectroscopy, electronic transitions that cannot be observed with ordinary UV spectroscopy (200-380 nm) are accessible; Rydberg transitions are just one example. FUV spectroscopy has been demonstrated to have unique and versatile applications. A variety of extensive application studies are now in progress, ranging from applications to fundamental science, such as studies of hydrogen bonding, hydration, and adsorption of water and aqueous solutions, to practical applications such as online, geochemical, environmental, and polymer film analyses. This review provides an introduction to, and brief history of, FUV spectroscopy, and describes the development of new FUV spectrometers, studies on electronic structure and transitions, its various applications, and future prospects.