TEMPERATURE-DEPENDENCE OF THE PROTON HYPERFINE INTERACTION IN HC60 AND THE PROTON-MUON HYPERFINE ANOMALY

The decrease in the proton hyperfine interaction of HC60 with increasi ng temperature is analyzed on the basis of quantum-chemical calculatio ns of the vibrational force field of the radical. The changes of the h yperfine interaction with respect to normal-mode displacements are eva luated and used to simulate the temperature dependence. It is shown th at the modulation by low-frequency A'' (C(s) symmetry) vibrational mod es of the radical that correspond to the lowest h(g) and h(u) vibratio ns of C60 dominates the observed temperature dependence. The experimen tally observed negative hyperfine anomaly, vis-a-vis the muon coupling , is also attributed to vibrational motions, specifically to the three modes that describe hydrogen motions.