MOLECULAR-DYNAMICS OF THE MUONIUM-C60 RADICAL IN SOLID C-60

The molecular dynamics and electronic structure of the muonium-C60 radical in crystalline C60 have been studied using muon spin rotation and relaxation. At room temperature muonium-C60 appears to be in a state of quasifree rotation. At the critical temperature T(s) = 260 K the local electronic structure and molecular dynamics change discontinuously as expected for a first-order phase transition. The correlation times for reorientation are remarkably close to those determined by recent NMR experiments on C60, suggesting that the molecular dynamics of muonium-C60 are strongly coupled to those of its C60 neighbors.