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A systematic description of the two-dimensional (2D) NMR exchange experiment for studying molecular motions in static powder samples is presented in terms of two-time distribution functions. Various angular distributions and their transformation to the NMR frequency domain yielding 2D absorption spectra are discussed. The concept of jump angle distributions is introduced. General and isotropic reorientation as well as different symmetries of the tensorial interaction between spin and lattice are distinguished in the analysis. Special attention is directed to the question, to what extent can angular information be reextracted from a 2D exchange spectrum without referencing any model of reorientation. For tensorial interactions of axial symmetry, projections of the 2D spectrum are also calculated and their usefulness is compared to that of the complete 2D spectra. The close relationship between the dynamic exchange experiment and several static NMR experiments like 2D separated local field spectroscopy of powders and NMR of oriented samples is pointed out.
Wefing et al. (Mon,) studied this question.