Evaluation of Distributed Hyperfine Parameters

Campbell, S. J.; Aubertin, F.

doi:10.1007/978-1-4899-2289-2_4

Cited by 14 publications

(11 citation statements)

References 179 publications

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“…To model spectra, fitting is typically done using computer software using a leastsquares fitting approach (71). Individual parameters can be floated or fixed to allow for the most realistic fit.…”

Section: Objectivesmentioning

confidence: 99%

“…This work focuses on high spin octahedrally coordinated (VI) Fe 2+ atoms, which largely narrows the scope of discussion. Several excellent review articles and books exist which thoroughly explore the theory, instrumentation , fitting, and applications in much greater depth than here (8,65,66,185,187). Mössbauer spectroscopy is predominantly done on the 57 Fe isotope, and the background presented will focus on this isotope.…”

Section: Background Mössbauer Spectroscopymentioning

confidence: 99%

“…As a result, the CS is often used to elucidate the electron density of the 57 Fe atom, which can then be applied to compare relative bonding environments and bond strengths. Because the 57 Fe isotope becomes smaller upon excitation by the γ-ray, the expected trend between electron density and the CS is reversed: an increase in CS indicates a decrease in s-electron density (8,71). When comparing high spin (HS) VI Fe 3+ and VI Fe 2+ atoms, the CS values are markedly different ( VI Fe 2+ : ~0.8-1.3 mm/s; VI Fe 3+ : ~0-0.5 mm/s) (8); the higher CS observed for Fe 2+ atoms is due to the extra d-electron having a probability of being closer to the nucleus than the s-electrons, which shields the s-electrons, and consequently reduces the s-electron density at the nucleus.…”

Section: Mössbauer Spectral Interpretationmentioning

confidence: 99%

“…The QS, or the electric field gradient (EFG), is caused by the nucleus having a non-spherical shape. For atoms with a nuclear spin (I) of ½ or greater (½ for 57 Fe), the nucleus can be elongated (rod-shaped) or flattened (pancake), with the QS being the measured deviation from spherical symmetry (71,190). Anisotropic effects in electron distributions, such as the increase in the strength of a bond, will increase the observed QS if it is increasing the distortion, or it will decrease the QS if it is counteracting the other distortions.…”

Section: Mössbauer Spectral Interpretationmentioning

confidence: 99%

“…Anisotropic effects in electron distributions, such as the increase in the strength of a bond, will increase the observed QS if it is increasing the distortion, or it will decrease the QS if it is counteracting the other distortions. When comparing HS VI Fe 2+ to VI Fe 3+ , the extra d-electron in VI Fe 2+ , which has an opposite spin of the other five d electrons, will occupy the lowest energy orbital, causing increased asymmetry in the electron density distribution, so the QS is typically much larger for HS VI Fe 2+ (~1.8-3.8 mm/s) than VI Fe 3+ (~0-1.0 mm/s) (71,185). It has been stated previously that the QS for HS VI Fe 2+ and VI Fe 3+ are temperature independent (185), although increasing QS with decreasing temperatures were observed in this study.…”

Section: Mössbauer Spectral Interpretationmentioning

confidence: 99%

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Redox behavior of magnetite in the environment

Gorski¹

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Magnetite (Fe 3 O 4) is a commonly found in the environment and can form via several pathways, including biotic and abiotic reduction of Fe 3+ oxides and the oxidation of Fe 2+ and Fe 0. Despite extensive research, the redox behavior of magnetite is poorly understood. In previous work, the extent and kinetics of contaminant reduction by magnetite varied by several orders of magnitude between studies, two fundamentally different models are used to explain magnetite oxidation (i.e., core-shell diffusion and redox-driven), and reported reduction potentials vary by almost 1 V. In other fields of science (e.g., physics), magnetite stoichiometry (x = Fe 2+ /Fe 3+) is a commonly measured property, however, in environmental studies, the stoichiometry is rarely measured. The stoichiometry of magnetite can range from 0.5 (stoichiometric) to 0 (completely oxidized), with intermediate values (0 < x < 0.5) referred to as nonstoichiometric or partially oxidized magnetite. To determine the relationship between magnetite stoichiometry and contaminant fate, the reduction rates of three substituted nitrobenzenes (ArNO 2) were measured. The kinetic rates varied over five orders of magnitude as the particle stoichiometry increased from x = 0.31 to 0.50. Apparent 15 N kinetic isotope effects (15 N-AKIE) values for ArNO 2 were greater than unity for all magnetite stoichiometries investigated, and indicated that mass transfer processes are not controlling the reaction rate. To determine if the reaction kinetics were redox-driven, magnetite open circuit potentials (E OCP) were measured. E OCP values were linearly related to the stoichiometry, with more stoichiometric magnetite having a lower potential, in good agreement with redox-driven models. The reaction of aqueous Fe 2+ and magnetite was investigated. Similar to previous findings for other Fe 3+ oxides, the formation of a stable sorbed Fe 2+ species was not observed; instead, the sorbed Fe 2+ underwent interfacial electron transfer to form a partially oxidized magnetite phase, which was accompanied by reduction of the viii TABLE OF CONTENTS LIST OF TABLES .

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Section: Objectivesmentioning

confidence: 99%