Rotating-frame level matching study of CH₃ tunneling in solid propionic acid

A study in the proton spin-rotating frame of the Zeeman-tunneling level matching of strongly hindered palmetic acid rotators CH₃ is reported. A set of consecutive spin-torsional matching resonances was employed to saturate the tunneling polarization. The observed tunneling saturation rate as a function of the rotating magnetic field strength gave a well-defined resonance peak when the Zeeman splitting was equal to one-half of the tunneling frequency. This peak defines the tunneling frequency accurately. At this resonance a bimodal process of polarization transfer occurs; a fast one driven by the intra-CH₃ proton-proton dipolar interaction and a slow one driven by the inter-CH₃ dipolar interaction.