MAGNETOOPTICAL STUDIES OF PHOTOEXCITATIONS IN C-61

We have used a variety of cw optical and optically detected magnetic-r esonance techniques to characterize long-lived photoexcitations in met hanofullerene (C-61) as a dispersion in polystyrene glass, at temperat ures below 10 K. We identify triplet excitons with zero-field-splittin g (ZFS) parameters D = 105 X 10(-4) cm(-1) and E = 9 X 10(-4) cm(-1). The triplet excitons are characterized by two photoinduced absorption (PA) bands in the triplet manifold at 1.5 and 1.7 eV, both with a life time of 160 mu sec, and a phosphorescence emission (PL) band with onse t at 1.85 eV and a lifetime of 10 mu sec. The difference in lifetimes between PA and PL is explained as being due to different recombination kinetics of the triplet sublevels. This and the finite axial symmetry ZFS parameter E not equal 0 compared to E=0 for triplets in C-60 show the lower symmetry of triplets in C-61, consistent with its postulate d distortions from icosahedral symmetry in the ground-state structure.