A line shape analysis of the effects introduced by motions in the nuclear magnetic resonance spectra of decoupled solids

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Abstract
An analysis of the effects of a two-site exchange process on the solid-state nuclear magnetic resonance (NMR) spectrum of an S spin coupled to an unlike I spin under rf irradiation is presented. It is shown that the line broadening that under certain conditions is shown by the S resonance can be calculated using a density matrix treatment. Although this approach has been used in order to evaluate the signal that arises from single crystallites, a simplification of the problem was introduced in order to evaluate the signal that arises from a powdered sample. With this approximation it was possible to evaluate the effects of exchange for a broad range of kinetic and decoupling conditions. The calculations were extended to include the effects of the chemical shift anisotropy of the S spins, and simulations obtained in this way agreed well with the experimental spectra of an exchanging solid recorded at different temperatures and decoupling fields. The relation between incoherent and coherent interference with decoupling in solids and in liquids is also briefly discussed.