Comparison of different theories for slowhyphen;tumbling axial nitroxide ESR hyperfine centers in polycrystallinehyphen;amorphous substances

摘要

The electron spinhyphen;resonance ESR hyperfine spectra computed by the Freed numericalndash;theoretical method have been critically compared with the recent analyticalndash;theoretical results for axially symmetric nitroxide ESR centers undergoing isotropic orientational diffusion motion in polycrystallinehyphen;amorphous substances. Consistent with the new analyticalndash;theoretical results, the dependencies of slowhyphen;motional line broadening and line shift on the associated orientational correlation time tgr; of the parallelhyphen;edge ESR centers determined from the Freed theoretical spectra are found to be tgr;minus;1/2within numerical computational limits. In addition to this tgr; dependence, the absolute magnitudes of the slowhyphen;motional line broadening and line shift are in reasonable agreement between the two theories. Except for the occurrence of some unexplainable extra lines in the Freed theoretical spectra, their overall powderhyphen;pattern structures are consistent with those computed by the analyticalndash;theoretical results.