The elusive OMu radical is believed to be formed by muonium reaction with nitrous oxide but has never been directly observed. It would be invisible to transverse-field muon spin rotation, so we propose identification and characterization by longitudinal-field repolarization, capitalizing on the characteristics of Hi-Fi to access the crucial level-crossing resonance and map out the field dependence of spin-lattice relaxation. Both the spectroscopy and dynamics would exhibit affects of strong spin-orbit coupling that are essentally unkown elsewhere in muSR spectroscopy.