Sign of the hyperfine parameters of anomalous muonium in diamond.

Observations with the muon-spin-rotation (..mu..SR) technique of the thermally activated transition from the isotropic muonium state Mu to the anisotropic muonium state Mu/sup */ in diamond are used to determine the sign of the Mu/sup */ hyperfine constants. It is found that the isotropic part of the Mu/sup */ hyperfine interaction is negative, indicating the importance of exchange polarization. The transition rate from Mu to Mu/sup */ follows an Arrhenius law over more than four decades. Finally, data are presented on the temperature dependence of the hyperfine interaction of isotropic Mu in diamond.