Proton Spin–Lattice Relaxation in Monocrystalline Ammonium Chloride

F.I. Bashirov
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引用次数: 4

Abstract

New symmetry-adapted autocorrelation functions are used in the theoretical description of the nuclear magnetic dipole–dipole relaxation in molecular crystals. They are obtained in the model frame that a molecule rotates by means of the finite angular jumps between the hindered states of the same symmetry in different potential wells. The experimental data of the temperature dependence of the proton relaxation timesT1andT1ρin the mono- and polycrystalline NH4Cl are revised. As a result, it is proposed to classify the NH+4ion motion by two kinds of the hindered states corresponding to the two-dimensional (E) and three-dimensional (F) irreducible representations of a point group of the cubic system. The dynamical weight of the stateFis defined to be equal to 0.25 and that of the stateEto be equal to 0.73 from the experiments in the ordered phase of NH4Cl. Based on abstract geometric groups, the respective weights are 0.4 and 0.6. This discrepancy in the weights of the states is explained by the effect of the tetragonal distortion of the tetrahedral site symmetry of the NH+4ion. The result of the prevalence of aC3reorientation in comparison to aC2reorientation of the ion is also justified. Because of the absence of the experimental temperature minima ofT1orT1ρ, assumptions are only made about the dynamical parameters of the NH+4ion motion in the disordered phase of NH4Cl.
单晶氯化铵中质子自旋-晶格弛豫
在分子晶体核磁偶极子-偶极子弛豫的理论描述中,引入了新的对称性自相关函数。它们是在分子旋转的模型框架中,通过在不同势阱中具有相同对称性的受阻态之间的有限角度跳跃得到的。修正了单晶和多晶NH4Cl中质子弛豫时间st1和t_1 ρ与温度关系的实验数据。因此,提出了用三次体系中点群的二维(E)和三维(F)不可约表示所对应的两种阻碍态来对nh4离子运动进行分类。在NH4Cl的有序相实验中,定义了态e的动态权值为0.25,态e的动态权值为0.73。基于抽象几何群,权重分别为0.4和0.6。这种态权值的差异可以用NH+4离子四面体位对称的四方畸变的影响来解释。与离子的ac2重取向相比,ac3重取向的普遍性也得到了证明。由于没有t1ort1ρ的实验温度最小值,所以只对NH4Cl无序相中nh4离子运动的动力学参数作了假设。
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