Abstract
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 KT m is dominated by spin diffusion of solvent protons and is independent of microwave frequency. Between about 130 and 170 K, 1/T m 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/T 1 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 inT 1 values at W-band and X-band supports this assignment.
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Fielding, A.J., Carl, P.J., Eaton, G.R. et al. Multifrequency EPR of four triarylmethyl radicals. Appl. Magn. Reson. 28, 231–238 (2005). https://doi.org/10.1007/BF03166758
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DOI: https://doi.org/10.1007/BF03166758