Quadrupole Couplings in Nuclear Magnetic Resonance, General
Quadrupole Couplings in Nuclear Magnetic Resonance, General
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核磁共振中的四极杆耦合，概述
DOI：
10.1002/9780470027318.a6111
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发表时间：
2006
影响因子：
5
通讯作者：
P. Man
中科院分区：
文献类型：
--
作者：
P. Man
核磁共振（NMR）光谱学不断发现新的应用。它使当地的对称性，以探讨在原子尺度上使用的核自旋I的化合物正在调查。核自旋是半整数（或奇数）或整数（或偶数）。元素周期表中的原子核可以分为两部分--自旋大于原子核和自旋大于原子核.自旋大于原子核的原子核被称为四极核，因为它们具有电四极矩，该电四极矩与其周围环境产生的电场梯度（EFG）相互作用。通过扩展，它们的自旋被称为四极自旋。自旋核对EFG不敏感.在具有自旋的原子核中，6%具有整数四极自旋，66%具有半整数四极自旋。
这篇文章的重点是半整数四极自旋（，和）在单晶和粉末化合物。这些自旋大多是可观察的。由于它们是多能级系统（能级数为2 I + 1），在由射频（RF）脉冲序列激发自旋系统期间发生多量子（MQ）跃迁。因此，需要量子力学的概念来理解自旋动力学和解释结果。特别是，脉冲序列的选择和实验条件，如脉冲持续时间，脉冲强度，和脉冲序列中的相位循环，取决于周围的核自旋的EFG的强度。
Nuclear magnetic resonance (NMR) spectroscopy is continually finding new applications. It enables the local symmetry to be probed at the atomic scale using the nuclear spins I of the compound under investigation. The nuclear spin is either a half-integer (or odd) number or an integer (or even) number. The nuclei in the periodic table can be divided into two parts – spin- nuclei and spin larger than nuclei. The spin larger than nuclei are called quadrupole nuclei because they possess an electric quadrupole moment which interacts with the electric-field gradient (EFG) generated by its surroundings. By extension, their spins are called quadrupole spins. Spin- nuclei are not sensitive to the EFG. Of the nuclei that possess a spin, 6% have integer quadrupole spins and 66% have half-integer quadrupole spins.
This article focuses on the half-integer quadrupole spins (, and ) in single crystals and in powder compounds. Most of these spins are observable. As they are multi-energy-level systems (the number of energy levels is 2I + 1), multiple quantum (MQ) transitions occur during excitation of the spin system by a radiofrequency (RF) pulse sequence. As a result, quantum mechanical concepts are needed for an understanding of the spin dynamics and for interpretation of the results. In particular, the choice of pulse sequence and the experimental conditions, such as pulse duration, pulse strength, and phase cycling in the pulse sequence, depend on the strength of the EFG surrounding the nuclear spin.