The effects of hindered rotation of the ammonium ion on nuclear magnetic spin–lattice relaxation

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Abstract
The reorientational mechanism of an ammonium ion, NH4 +, in a solid is modeled as two independent stochastic Poisson processes corresponding to the twofold and threefold reorientations. Autocorrelation functions and the associated power spectra are calculated on this basis and applied to the development of expressions for the proton spin–lattice relaxation times in the laboratory and rotating frames. Certain special cases are considered and some conclusions drawn for the analysis of reorientational mechanisms from nuclear magnetic spin–lattice relaxation results.