Tunneling Spectroscopy from Magnetization Evolution in a Tilted Rotating Frame of Nuclear Spins

The time evolution of the proton Zeeman magnetization in the rotating frame at the magic angle θM = cos−1(1/3) is calculated for an isolated tunneling methyl group and its Fourier transform is given. The calculation compares well with the experimental spectra of CH3CD2I and methylmalonic acid. It is shown that Fourier transform spectroscopy of the magnetization evolution in a tilted RF frame represents an excellent alternative to the analogous experiment performed at exact resonance, resulting in improved resolution and a much better signal-to-noise ratio.