C-13-NMR was employed to study C60 molecular dynamics in pure C60 crys
tals prepared by sublimation technique and by evaporation of CS2-solut
ion of C60. The C60 molecular dynamics in the CS2-grown crystal with o
rthorhombic (OR) structure was significantly changed by heat-treatment
s. This behavior was assigned to a structural conversion of OR to FCC
(face centered cubic) by heat-treatment and also to annealing effect o
f defects in the crystal. C70 molecular dynamics was also studied in P
ure C70 crystal. The C70 molecular rotation was found to be more restr
icted than those of C60 molecule in the crystals. It was suggested tha
t an anisotropic molecular rotation is dominant below approximately 28
0K in the time scale of NMR line width (approximately 20musec).