Relaxation of Multiple Quantum NMR Coherences in Quasi-One-Dimensional Spin Systems

Abstract

Abstract Dynamics and relaxation of the multiple quantum (MQ) NMR coherences of the zeroth and second orders are studied experimentally and theoretically in a quasi-one-dimensional chain of nuclear spins 19F in calcium fluorapatite. The dependencies of the intensities of those coherences on the time of the preparation period of the MQ NMR experiment is obtained. A good agreement of the experiment with theoretical predictions is demonstrated. Dipolar relaxation of the MQ NMR coherences is investigated on the evolution period of the MQ NMR experiment. A theory of dipolar relaxation of the MQ NMR coherences is developed for the model in which only the ZZ part of the secular dipole–dipole interactions is taken into account (ZZ model). It is shown that the MQ NMR coherence of the zeroth order is not subject to dipolar relaxation in the ZZ model. The experimental data qualitatively agree with the results of the developed theory for the MQ NMR coherence of the second order.