Spin diffusion of methyl protons in sodium and lithium acetates

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Abstract
The transfer of nuclear magnetisation between the spectral components of CH3 protons is studied in single crystals of CH3COONa.3D2O and CH3COOLi.2D2O from 4.2 K to 300 K. The results support a model derived for the methyl-proton spin diffusion (also called spectral diffusion) by time-independent dipolar transitions. Two independent processes are predicted and verified in sodium acetate under conditions that hold above 20 K. At 10 K the lattice-dependent processes dominate but at still lower temperatures the magnetisation transfer is again independent of motion. The influence of rotational tunnelling on spin diffusion is demonstrated in lithium acetate at 4.2 K.