化学位移张量的测量

对于刚性晶格中的分子，化学位移是与外加磁场空间取向相关的张量，这个张量有6个独立的分量. 化学位移张量也可以利用其主轴分量及主轴与晶体坐标系的方向余弦来表示. 很显然，知道了固体分子中各不等价位置处的化学位移张量，就可以推测出分子中电子分布的图象，具有重要意义. 本文首先描述了化学位移张量测量的理论，对测量化学位移 各 向异性的各种方法作了介绍和比较，并详细论述了一些常用的方法，如二维魔角跳旋转(M a gic Angle Hopping, MAH)、二维魔角慢旋转(Magic Angle Turning, MAT)和二维变相旋转边带分离（2D phase-adjusted spinning sidebands, 2D-PASS）技术等. 最后，还介绍了单晶化学位移张量的常规测量方法.

MEASUREMENT OF CHEMICAL SHIELDING TENSOR

In rigid lattice, chemical shift is a tensor depending on the spatial orientation of the external magnetic field. The tensor has six independent components. The orientation of chemical shielding tensor can be expressed with direction cosines of its principal axis system. It is of great interest that if the chemical shift tensor of each nonmagnetically equivalent nucleus is known, the information on the distribution of the electron cloud in the molecule can be deduced from these tensors. In this paper, the theory and methods of measurement of chemical shift tensor are reviewed. A number of common methods are discussed in detail, such as 2D magic angle hopping (MAH), 2D magic angle turning(MAT), and 2D phase-adjusted spinning sidebands(2D-PASS) technique and so on. The common methods for measuring single crystal chemical shielding tensor are also discussed.