Radical magnetic fields

Figure Bl.15.6. The EPR spectrum of tire perinaphthenyl radical in mineral oil taken at room temperature. (A) First derivative of the EPR absorption x with respect to the external magnetic field, Bq. (B) Integrated EPR spectrum.

Even for a single radical tire spectral resolution can be enlianced for disordered solid samples if the inliomogeneous linewidth is dominated by iimesolved hyperfme interactions. Whereas the hyperfme line broadening is not field dependent, tire anisotropic g-matrix contribution scales linearly with the external field. Thus, if the magnetic field is large enough, i.e. when the condition... 

The first temi describes the electronic Zeeman energy, which is the interaction of the magnetic field with the two electrons of the radical pair with the magnetic field, Bq. The two electron spins are represented by spin... 

Electron-transfer reactions producing triplet excited states can be diagnosed by a substantial increase in luminescence intensity produced by a magnetic field (170). The intensity increases because the magnetic field reduces quenching of the triplet by radical ions (157). 

A pictorial representation of the Tg-S mixing process follows from Fig. 6. Just as in normal n.m.r. or e.s.r. spectroscopy, precession can be represented by a vector model. When placed in an external magnetic field the two unpaired electrons of the radical pair 1 and 2 will precess... 

Here and H describe radicals A and B of the radical pair and He the interaction of their electrons. The other terms in equation (15) are H g, the spin orbit coupling term, H g and Hgj, representing the interaction of the externally applied magnetic field with the electron spin and nuclear spin, respectively Hgg is the electron spin-spin interaction and Hgi the electron-nuclear hyperfine interaction. 

Magnetic Field Effects on the Dynamics of the Radical Pair in a Cgo Clusters-Phenothiazine System... 

MFEs on the dynamics of the radical pair in CtoN" clusters (C oN " ) -MePH system were examined in TH F-H2O (2 1) mixed solvent. M FEs on the decay profiles of the transient absorption at 5 20 nm due to the phenothiazine cation radical (P H " ) are shown in Eigure 15.9b. The decay was retarded in the presence of the magnetic field. In addition, the absorbance at 10 (is after laser excitation increased with increasing magnetic field. The result indicated that the yield of the escaped PH increased with the increase in magnetic field. Therefore, the MFEs on the decay profile were clearly observed. 

Yonemura, H., Kuroda, N., Moribe, S. and Yamada, S. (2006) Photoindiced electron-transfer and magnetic field effects on the dynamics of the radical pair in a Cgo clusters-phenofhiazine system. C. R, Chim., 9, 254-260. 

Haidar, M Misra, A., Banerjee, A. K. and Chowdhury, M. (1999) Magnetic field effect on the micellar (C)-pyrene- radical-pair system. J. Photochem. Photobiol. A, 127, 7-12. 

HYSCORE spectra of zeaxanthin radicals photo-generated on silica-alumina were taken at two different magnetic fields B0=3450G and B0=3422G, respectively. In order to combine the data from the two spectra, the field correction was applied (Dikanov and Bowman 1998). The correction consists of a set of equations that allow transformation of spectra to a common nuclear Zeeman frequency. The set of new frequencies was added to that of the former spectrum and plotted as the squares of the frequencies v2a and v2p. Examples of these plots can be found in Focsan et al. 2008. 

Figure 4 ESR of nitroxide radicals (a) Molecular axes of the nitroxide (b) ESR spectra of oriented nitroxide radicals, with the molecular axes x, y, and z along the external magnetic field, respectively and (c) ESR spectra of randomly oriented nitroxide radicals motionally averaged (upper) and rigid limit (lower) regimes.

Figure 6 Simulated ESR spectra of nitroxides (a) in the absence of magnetic field gradient (b) ID image for a homogenous radical distribution (in the presence of a gradient) and (c) ID image for radicals present only in thin layers near both surfaces of the plaque (in the presence of a gradient).

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