Muon Spin Resonance of Radicals on Surfaces

Polarized positive muons are incorporated as spin labels in organic free radicals adsorbed on large-area surfaces. Two muon spin resonance techniques are introduced which allow the detection of the muonanted species, either in transverse or near avoided crossings of energy levels in longitudinal magnetic fields. The radicals are characterized by their hyperfine interactions, and dynamic information is obtained from the extent of averaging of the hyperfine anisotropy. Because of the high spin polarization the method is extremely sensitive and allows the study of radicals at concentrations down to a single radical in the sample at a given time, and therefore under conditions of high mobility where conventional techniques often fail due to radical termination reactions.