NMR cross-relaxation study of ultraslow motion of the domain wall in channel inclusion compound

We report on an NMR study of ultraslow motions in the channel thiourea-hexachloroethane inclusion compound, [2.95(NH2)(2)CS].C2Cl6. Temperature dependent H-1 NMR relaxation measurements of the powder thiourea-hexachloroethane at different resonance frequencies, from 23 to 55.5 MHz, have been carried out. Significant reduction of the spin-lattice relaxation time at 38 and 47 MHz is caused by the cross-relaxation of protons via the quadrupole chlorine nuclei. We show that the effective H-1-Cl-35 cross-relaxation observed in a powder sample is due to a slow mode process, when the molecules of the domain wall exhibit a correlated translational and rotational motion over the channel. Such propagation of the domain wall is confirmed by atom-atomic potential calculation. - Pacs: 76.60-k, 76.60.Es, 61.44.Fw, 61.66.Hq.