Short-wavelength (λ < 160 nm) Raman spectroscopy offers an advantage of a generally higher sensitivity than Raman spectroscopy in the visible range. An application with high potential is its use for environmental water analysis targeting archetypal compounds that are present in industrial and urban sewage water. However, this application is feasible only if specific performance benchmarks are met. We validate the applicability of a simple and cost-effective deep-UV Raman spectrometer (λexc = 236.5 nm). The analysis brings to the fore that the experimentally derived detection limits the studied archetypal compounds are to high by several orders of magnitude. We outline potential further development and associated limitations. These are the deterioration of the analysed species by photolysis as a consequence of the high photon energy and intensity, and the self absorption of the UV radiation. These effects are explained and partially corrected along a simple mathematical model from which a general limit of detection is estimated.
Deep-UV Raman spectroscopy is a promising method for the analysis of nitrates and nitrites in water at ppm (mg/l) concentrations. In addition to the high sensitivity, the tunability of the laser source allows to deeper investigate the photoinduced reactions taking place under deep-UV illumination. Under these conditions, nitrate ions decompose into oxygen and nitrite through different reaction pathways. Analysis of the evolution of nitrate and nitrite Raman modes as a function of the excitation wavelength allows for estimating the photo-energy dependent quantum yield of the photolysis process. The results highlight the limits and capabilities of deep UV Raman as a on-line nitrate and nitrite monitoring method.
X-ray absorption spectroscopy (XAS) is a widely used technique for determining the electronic structure of matter. In contrast to X-ray photoelectron spectroscopy (XPS), XAS makes use of photons only, and therefore suffers less from absorption of the probe beam, i.e., electrons or photons, respectively. This is true for hard X-rays probing, e.g., the Kedges of d-metals in metal hydrides (albeit with limited chemical information). Soft X-rays, which are suited to analyze the electronic structure of hydrogen in solids, have a limited absorption length in gases. Photons with energies of less than 50 eV (“hydrogen K-edge” <;20 eV) are absorbed in less than 1 mm at ambient pressure, which is needed for technical hydrides. Recently, we developed a membrane-based approach to study materials exposed to high hydrogen “pressures” while keeping analysis chamber under high vacuum - thus effectively achieving high pressure XPS analysis. In this paper, we demonstrate that the membrane approach originally designed for XPS can be equally well used for XAS. We show first results on the electronic structure of hydrogen in Pd-Ag alloy as measured by in situ XAS using a laboratory extreme ultraviolet (EUV) source.
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