Determination of hyperfine interactions from the magnetic field dependence of nuclear modulation frequencies: An electron spin echo envelope modulation study of protons in. gamma. -irrradiated potassium dihydrogen arsenate

Journal Article · Mon Oct 01 00:00:00 EDT 1990 · Journal of Chemical Physics; (USA)

DOI:https://doi.org/10.1063/1.458697· OSTI ID:6530499

Gerfen, G J; Singel, D J ^[1]

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1. Department of Chemistry, Harvard University, Cambridge, MA (USA)

A study is presented of the field dependence of proton ESEEM (electron spin echo envelope modulation) of the AsO{sup 4{minus}}{sub 4} center in {gamma}-irradiated single crystals of KDA (potassium dihydrogen arsenate). Modulation patterns and corresponding spectra were registered over the range of external field strengths spanned by the nominally allowed EPR transitions ({similar to}3.5 kG) with the field orientation selected along the crystallographic {ital c} axis. By tracking the external field dependence of the ESEEM frequencies of the protons attached and hydrogen-bonded to the AsO{sup 4{minus}}{sub 4} center, the absolute value of both the secular and nonsecular portions of their hyperfine interactions, as well as the sign of the secular component, are determined. The results are compared with those obtained by ENDOR (electron-nuclear double resonance) spectroscopy. The implications of this work for the determination of the magnitudes and signs of the elements, principal values, and direction cosines of the principal axes of hyperfine interaction matrices in orientationally disordered solids are discussed in detail. The large hyperfine coupling to the {sup 75}As nucleus has important ramifications upon the ESEEM spectroscopy and its analysis. In general, such couplings increase the breadth of the EPR spectrum and thereby facilitate the survey of ESEEM field dependences; they can also seriously complicate the analysis of the ESEEM results by precipitating significant deviations between the magnitude of the expectation value of the electron spin angular momentum and its nominal value, {ital M}{sub {ital S}}: ESEEM frequency expressions in which these two quantities are implicitly equated are not generally applicable. This issue is commented on in detail.

• OSTI ID: 6530499
• Journal Information: Journal of Chemical Physics; (USA), Journal Name: Journal of Chemical Physics; (USA) Vol. 93:7; ISSN JCPSA; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEAR CHEMISTRY
400600* -- Radiation Chemistry
ALKALI METAL COMPOUNDS
AMINES
AMMONIUM COMPOUNDS
ANIONS
ARSENATES
ARSENIC COMPOUNDS
ARSENIC OXIDES
CHALCOGENIDES
CHARGED PARTICLES
CHEMICAL BONDS
CHEMICAL RADIATION EFFECTS
CHEMICAL REACTIONS
CHEMISTRY
DECOMPOSITION
ELECTROMAGNETIC RADIATION
ELECTRON SPIN RESONANCE
GAMMA RADIATION
HYPERFINE STRUCTURE
INTERACTIONS
IONIZING RADIATIONS
IONS
MAGNETIC FIELDS
MAGNETIC RESONANCE
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
POTASSIUM COMPOUNDS
QUATERNARY COMPOUNDS
RADIATION CHEMISTRY
RADIATION EFFECTS
RADIATIONS
RADICALS
RADIOLYSIS
RESONANCE
SPIN ECHO