An attenuated total reflectance far-UV spectrometer

Abstract

An ultraviolet spectrometer based on attenuated total reflection (ATR) has been developed and tested for liquid water (light and heavy water) in the wavelength range from 140 to 300 nm, which includes the far ultraviolet (FUV) region. One of the principal limitations of FUV transmission spectra is the strong absorption of the solvent itself. High absorptivity of the n --> sigma(*) transition in water molecule has thus far prevented meaningful spectral measurements of aqueous solutions in the wavelength region under 170 nm. Our technique uses the evanescent wave created through total reflection when light is passed through an internal reflection element (IRE) in contact with the sample. Since the evanescent field is used as an optical path length, the method allows spectral measurements favorably comparable with that of transmittance method with a shorter path length than the wavelength of FUV light. In this study, we have designed an original miniature IRE probe made of sapphire that allows detection of the whole n --> sigma(*) transition absorption band of water down to 140 nm. The obtained ATR-FUV spectra closely match calculations based on the Fresnel formula. It is also confirmed that this spectrometer is equally effective for spectral measurements of nonaqueous solvents with significant absorptivities in the FUV region.

Total internal reflection spectroscopy for studying soft matter

“…None-the-less, ATR accessories for UV-visible spectrometers are commercially available. The principal application of ATR UV-vis spectroscopy is to systems where a long path length is challenging, due either to high turbidity of a suspended catalyst, 58 or to strongly absorbing materials such as solvents (in the UV) 59 or dyes. …”

Far‐Ultraviolet ( FUV ) Spectroscopy in the Solid and Liquid States, Principle, Instrumentation, and Application of

“…(25,36,40,43) We describe later the application of FUV spectroscopy for the qualitative and quantitative analyses of aqueous solutions. The foot of this band, which can be observed in the 190-210 nm region by using an ordinary UV-Vis spectrometer, is also useful for the qualitative and quantitative analyses.…”

“…(1) To overcome the difficulty in liquid-and solid-state FUV spectroscopy, we recently developed two kinds of FUV spectrometers with quite different designs. (31,43) One is a compact FUV spectrometer by which one can measure spectra of liquid samples down to 180 nm with nitrogen gas purge. (31) Its size is only 30 cm ×16 cm ×16 cm, including a UV light source, a grating, a photo absorption cell, and an optical sensor.…”

“…The other is an ATR-FUV spectrometer that covers the wavelength range from 140 to 300 nm. (43) In this spectrometer, the design of a very small internal reflection element (IRE) probe has led to successful measurement of a wholẽ A ←X transition absorption band of water and aqueous solutions.…”

“…(43) Figure 6(a) illustrates a portion of the custom design of a commercial FUV spectrometer (KV-200, Bunkou-Keiki, Hachioji, Japan). Figure 6(b) depicts a flow cell unit formed between the sapphire IRE probe (7) and a fluorinated resin holder (8) enlarged from the marked area in Figure 6(a).…”