RADIOFREQUENCY MUON SPIN-RESONANCE STUDIES OF ENDOHEDRAL AND EXOHEDRAL MUONIUM ADDUCTS OF FULLERENES

The radio-frequency muon spin resonance technique (RF-mu SR) is descri bed, with examples drawn from muon studies of fullerenes. Two distinct species can be detected by RF-mu SR when solid C-60 is irradiated wit h positive muons. Endohedral muonium (Mu@C-60) is characterized by a m uon hyperfine constant (A(mu)) close to the vacuum value. A remarkable feature of the RF-mu SR spectrum is the double quantum transition, wh ich appears when the allowed transitions are saturated. The exohedral muonium adduct (C(60)Mu) is also detected, and has a much smaller valu e of A(mu), typical of a carbon-centred organic radical. It has been s tudied by RF-mu SR in dilute solution, which is not possible for trans verse field muon spin rotation (TF-mu SR). There is a significant diff erence in A(mu) of C(60)Mu in the solid and in solution, a result of g reat import to the analysis of avoided-level crossing experiments on ( 13)C(60)Mu.