Extended X-ray absorption fine structure

About: Extended X-ray absorption fine structure is a research topic. Over the lifetime, 10452 publications have been published within this topic receiving 276744 citations.

Empirically determined infrared absorption coefficients of H2O from 300 to 3000°K

Abstract: A set of absorption coefficients for water vapor as functions of temperature has been empirically deduced from existing quantitative absorption and emission spectra between 1 and 22 micro. The basic assumption was made that, for optically thick gases, the curve of growth is given by a statistical model. The absorption coefficients were obtained for each vibration-rotation band by adjusting the band averaged line half widths and line spacing such that the integral of the absorption coefficients was equal to the known integrated intensity of the particular band at a given temperature. The effect of foreign gas broadening and non-resonant water molecule broadening was included. The present results are compared with independent theoretical and experimental results and the agreement is satisfactory.

Electronic and structural investigations of technetium compounds by x-ray-absorption spectroscopy

Abstract: X-ray absorption near edge structure spectroscopy has been used to establish the chemical shifts of the technetium K edge in a range of compounds containing Tc in a variety of formal oxidation states. The edge positions span 19.9 eV from Tc metal to NH{sub 4}TcO{sub 4}. Strong correlation between chemical shift and formal oxidation state is observed. Extended X-ray absorption fine structure (EXAFS) spectroscopy of Tc{sub 2}(CO){sub 10} indicates that multiple scattering along the Tc-C-O vector is more important than direct Tc{center_dot}{center_dot}O scattering. TcO{sub 2} is shown by EXAFS to possess a distorted rutile structure with a closest Tc-Tc distance of 2.61 {Angstrom}. This is rationalized in terms of the Goodenough model for bonding in transition metal dioxides.

EXAFS studies of pentavalent neptunium carbonato complexes. Structural elucidation of the principal constituents of neptunium in groundwater environments

Abstract: Neptunium is the most problematic actinide element with respect to environmental migration because its solubility under typical groundwater conditions is expected to be high enough to be radiological concern, and its sorption on common minerals is expected to be relatively low Neptunium solubility in carbonate solutions is controlled by the formation of solids of general formula M{sub 2n-1}NpO{sub 2}(CO{sub 3}){sub n}, whose features have been reviewed The limited solubilities (10{sup -4}-10{sup -7} M) of these phases make the solution species in equilibrium with the solids very difficult to study using common structural methods We find that alkali free synthesis employing the tetrabutylammonium (TBA) cation provides 10{sup -3} M solutions of NpO{sub 2}(CO{sub 3}){sup -} and NpO{sub 2}(CO{sub 3}){sub 2}{sup 3-} These relatively high solubilities are unprecedented and afford the opportunity to determine the molecular structures of these environmentally important complexes employing EXAFS spectroscopy The near-IR absorption spectra of the neptunium electrolyte solutions are nearly identical, indicating that the same species are present in both solutions Known thermodynamic constants were used to prepare single-component solutions, and near- IR spectra were measured both before and after EXAFS analysis to confirm that each solution sample contained a single, pure neptunyl carbonato species 19more » refs, 1 fig, 1 tab« less