OBSERVATION OF ENDOHEDRAL MUONIUM IN C61H2

A study is presented of endohedral muonium (Mu = mu(+)e(-)) in a funct ionalized fulleroid, the 6, 5 isomer of C61H2. The temperature indepen dence of the muonium depolarization rate implies that in the timescale of the mu SR experiment no isotropic reorientation regime sets in eve n at 280 K. The depolarization appears dominated by the interaction of Mu with methylene protons. No anisotropy of the hyperfine interaction was directly detected within experimental accuracy; an upper limit fo r the anisotropy can be fixed to 600 kHz by a transverse field measure ment.