抄録
The anisotropy of the spin-lattice relaxation time T1D of dipolar energy, that T1ρ in the rotating frame and that T1 in the high magnetic field have been studied in tetrahedrally coordinated four-spin-1/2 system. The expression of T1D and T1ρ is presented when tetrahedron reorientates about the four three-fold axes and three two-fold axes. The anisotropy of T1D and T1ρ of proton spins in NH4Cl and NH4Br has been measured and compared with the present model of relaxation times. The measurement of T1ρ is more useful because of the larger anisotropy to determine the model of the reorientation of NH4-ion than that of T1D and T1. The present model is in good agreement with the experimental results in NH4Cl, but the agreement is worse in NH4Br. Some possible origins for the disagreement in the latter case are discussed. We have also compared the present model of spin-lattice relaxation times with those which were derived by the other authors.
