Orientational dependencies of dynamics and relaxation of multiple quantum NMR coherences in one-dimensional systems

[Display omitted] •Dynamics/relaxation of MQ NMR coherences are investigated at different orientations.•The relaxation of the MQ NMR coherences is determined by dipole-dipole interactions.•The universal time scale for different orientations was obtained. Dynamics and relaxation, or decoherence, of multiple quantum (MQ) coherences are investigated experimentally and theoretically for different orientations of a single crystal of fluorapatite with respect to the external magnetic field. Dynamics of MQ coherences is studied as a function of the preparation period of the MQ NMR experiment. Their relaxation, or decoherence, during the evolution period is also investigated. Universal curves for dynamics and relaxation are obtained and describe the experimental data for different orientations of the investigated sample. Those curves prove the dipolar nature of the observed relaxation process. The contribution of the heteronuclear interactions to the dipolar relaxation is also investigated. The source of discrepancies between experimental data and theoretical results in the experiments with a large angle between the nuclear spin chains and the external magnetic field are discussed.