Multifrequency EPR of four triarylmethyl radicals

A. J. Fielding, P. J. Carl, G. R. Eaton, S. S. Eaton

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    Continuous-wave spectra at W-band of four triarylmethyl (trityl) radicals at 100 K in 1:1 water-glycerol exhibit rhombic electron paramagnetic resonance spectra. The rigid-lattice line widths at W-band are only 3 to 5 times larger than at X-band or S-band, and fluid-solution line widths are much narrower than those for rigid lattice, which indicates that unresolved anisotropic nuclear hyperfine couplings make significant contributions to the rigid-lattice line widths. Spin-flip lines are observed in glassy-solution spectra at X-band and S-band, but not at W-band or 250 MHz. At 100 K Tm is dominated by spin diffusion of solvent protons and is independent of microwave frequency. Between about 130 and 170 K, 1/Tm for trityl-CH3 is enhanced by rotation of the methyl groups at a rate comparable to inequivalences in the hyperfine interaction. Motional averaging of anisotropic interactions enhances spin echo dephasing between about 200 and 300 K. The temperature dependence of 1/T1 is similar for the four radicals and is consistent with assignment of the Raman process and a local mode as the dominant relaxation processes. The similarity in T1 values at W-band and X-band supports this assignment. © Springer-Verlag 2005.
    Original languageEnglish
    Pages (from-to)231-238
    Number of pages7
    JournalApplied Magnetic Resonance
    Issue number3-4
    Publication statusPublished - 2005


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