13C hyperfine coupling constants of the MuC60 radical have been measured by muon level-crossing spectroscopy, using a dilute solution of 99% enriched 13C60 in decalin. The signs as well as the magnitudes of the hyperfine constants were determined. The results range from 52.6 to −25.4 MHz and support those calculations which predict an extended distribution of unpaired electron spin density in radical adducts of fullerenes. The hyperfine constants are consistent with published electron spin resonance results for (CD3)3CC60, but contradict a recent report for HC60, where a considerably smaller value is reported for the largest splitting. [ABSTRACT FROM AUTHOR]
