Second order rate constants and cidep enhancements of transient radicals in solution by modulcation ESR spectroscopy
1976; Elsevier BV; Volume: 15; Issue: 1 Linguagem: Inglês
10.1016/0301-0104(76)89011-8
ISSN1873-4421
Autores Tópico(s)Photochemistry and Electron Transfer Studies
ResumoThe theory of modulation ESR (MESR) spectroscopy is extended to spin systems exhibiting second order or mixed first and second order decays and electron spin polarization effects. Analytical solutions for the dependence of the Fourier components of the ESR signal on the modulation frequency and the initiation rate are derived. They allow a determination of the types of decay, of the decay rates, and of the polarization enhancement factors and are applied to experimental MESR results obtained from two transient radical systems. It is shown that the bimolecular terminations of hydroxymethyl in methanol and α-tetrahydrofuryl in THF are diffusion controlled. Electron spin polarization effects of α-tetrahydrofuryl are shown to be due to nonreactive biradical collisions. The polarization pattern is in qualitative accord with microscopic theories, which, however, fail to reproduce the absolute enhancements by factors of 2 to 3.
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