SPECTRAL SPIN-DIFFUSION OF A SPIN-3/2 SYSTEM IN ROTATING SOLIDS

Spectral spin diffusion involving spin-3/2 quadrupolar nuclei in a polycrystalline sample under magic-angle spinning is investigated for the first time. The polarization transfer between the central transitions of two chemically inequivalent quadrupole spins, in polycrystalline sodium tetraborate decahydrate, Na2B4O7 . 10H(2)O, driven by the abundant proton environment, was explored both theoretically and experimentally. Cross peaks in the two-dimensional spectrum arising from spin diffusion between two inequivalent Na-23 sites were observed. The dependence of the spin diffusion rate upon the sample spinning speed is discussed. Because of the strong quadrupolar interactions which dominate the relaxation process, the intensities of the cross-peaks from spin diffusion are reduced. The effect of anisotropies of the interaction parameters on the line shape and diffusion rate were studied and are fully explained by the theoretical treatment given.