Sideband Patterns in Dynamic-Angle-Spinning NMR

It is known that dynamic-angle-spinning (DAS) NMR can be accomplished using a variety of complementary angles (θ 1, θ 2) characterizing the two orientations of the spinner axis with respect to the magnetic field. In cases where the evolution period of the two-dimensional DAS experiment is divided into unequal parts, for example, by RF pulses or spinner reorientation, a complex sideband pattern emerges. We describe a simple theory of the sideband pattern and provide illustrative experimental results of spectra over a range of DAS angles. The DAS experiment with the angle pair (0°, 63.43°) has sidebands at integer multiples of 0.83Ω R and should be particularly useful for DAS cross-polarization experiments involving central transitions of quadrupolar nuclei. Our considerations are relevant to other NMR experiments in which an evolution time is composed of periods separated by a perturbation and/or characterized by different effective Hamiltonians.