Tunneling spectroscopy by matching energy levels in the spin-rotating frame

Tunneling spectra of strongly hindered (Formula presented) in methylmalonic acid, dimethyl sulfide, propionic acid, and hexane are reported. The Zeeman-tunneling level-matching resonances are detected at (Formula presented) 1, and 2 when the level matching is maintained for 10 ms in the 54.7° tilted proton spin-rotating frame. A ground-state manifold of two noninteracting but equivalent methyl groups accounts for these spectra. All the transitions, which bring about the population equalization whenever a matching resonance occurs, are driven by time-independent dipole-dipole interactions. The resonance peaks at (Formula presented) and (Formula presented) which are observed in a tilted rotating frame only, indicate that pairs of methyl groups undergo a symmetry conversion simultaneously. The calculated magnetization changes, which are the consequence of population equilibration, reproduce the observed resonance peaks intensities well.