Temperature Dependence of the ESR Spectrum of CO2−CF2CFCO2− in Irradiated Sodium Perfluorosuccinate

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Abstract
Irradiated single crystals of sodium perfluorosuccinate show ESR spectra at 300°K characteristic of a single CO2−CF2CFCO2− radical, but on cooling below 130°K the spectra show that motion has been frozen out and that the radicals occupy two crystallographically nonequivalent positions. The hyperfine interaction tensors for one α‐ and two β‐fluorine atoms of each radical have been determined at 77°K and compared with those of the 300°K radical. The average of the hyperfine tensors for the two radicals at 77°K is shown to be close to the observed tensor for the single radical at 300°K. Motional averaging by oscillation about the central C–C bond is indicated. Crystals of sodium perfluorosuccinate irradiated and observed at 77°K without warming up show the presence of a single radical with a somewhat different orientation in the crystal lattice than the room temperature radical or either of the radicals obtained on cooling the room temperature radical to 77°K.