![]() The biradical studied is shown in the above reference, and in Ref. The given error is obtained from the change in the calculated distance when one frequency standard deviation is subtracted from the mean frequency. The given error is the standard deviation of 20 observations. (Frozen solution EPR yields, g | = 2.0024 and A | = 90.7 MHz. In fact, the characterization of this system as axial is itself an approximation, since most nitroxide radical are at least slightly rhombic. They are, however, estimated and not fit values. These parameter values were judged to reasonably reproduce the width and line shape of the frozen solution cw EPR spectrum. ![]() Rozantsev, Free Nitroxyl Radicals, edited by B. The absolute value of frequency can be taken in a subsequent step. As written, I(ω αβ) can take on both positive and negative frequency values. Abragam, Principles of Nuclear Magnetism (Oxford U.P., New York, 1961). Inasmuch as the integrated area is expected to scale with the echo intensity for most common echo shapes, this assumption should have a negligible impact on the final outcome. It is more typical, however, to integrate over some boxcar width. ![]() This equation assumes observation at time 2τ′. Mims, in Electron Paramagnetic Resonance, edited by S. This complete spectral overlap is certainly true for the symmetric biradical studied here it is a good approximation for most nitroxide biradical systems (unless isotopically substituted to form a 14 N − 15 N biradical pair). If sin γ = 0, X ̂ can be any arbitrary vector perpendicular to Ẑ, and Y ̂ = Z ̂× X ̂. 32 and 33) can lead to a phase shift of the A-spin-echo. As the resonance frequency difference approaches the microwave field strength of the ω 2 pulse, Bloch-Siegert (Refs. This selective excitation of the A spins implicitly assumes (ω 1 −ω 2 )>ω R 0 >ω AB, in which ω R 0 is the Rabi frequency on resonance. Schmidt (Koninklijke Nederlandse Akademie van Wetenschappen, Amsterdam, 1989), pp. Tsvetkov, in Pulsed EPR: A New Field of Application, edited by C. 23, 59 (1982) Google ScholarĮnglish translation I. Eaton, in Biological Magnetic Resonance, edited by L. 12 for further discussion and examples of this phenomenon. This situation applies both when the relevant internuclear distances are small or when the electron spin associated with the chosen probes sustains appreciable derealization. At smaller interelectron spin separations, exchange interactions that are difficult to distinguish from the magnetic dipole couplings can contribute to the total electron-electron spin interaction, and thus complicate distance determinations. Kevan, Time Domain Electron Spin Resonance (Wiley Sons, New York, 1979), pp.
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