Electron paramagnetic resonance study of atomic phosphorus encapsulated in[60]fullerene

Well resolved EPR spectra of P@C-60 in solution have been recorded, proving that the encased phosphorus atoms are in their quartet spin ground state. The isotropic hyperfine interaction is increased by a factor of 2.5 compare d with the values measured for free atoms. An analysis of spin relaxation d ata reveals that fluctuating zero field splitting (ZFS) interaction induced by collision-induced deformations of the carbon shell constitutes the domi nant relaxation mechanism. The variance of the time fluctuating ZFS interac tion is about a factor of 10 larger than that observed for N@C-60 under ide ntical conditions. Values for the correlation time of the deformation of th e fullerene cage range from 5 ps to 32 ps in the temperature interval 190-3 00 K in toluene.