Determination of the absolute sign of nuclear quadrupole interactions by laser radio-frequency double-resonance experiments.
Determination of the absolute sign of nuclear quadrupole interactions by laser radio-frequency double-resonance experiments.
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通过激光射频双共振实验确定核四极相互作用的绝对符号。
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发表时间：
1993
期刊：
影响因子：
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通讯作者：
Suter
中科院分区：
文献类型：
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作者：
Blasberg;Suter
核自旋I > +的四极矩与电场梯度张量之间的相互作用导致核自旋态的能量分裂。我们展示了如何激光和射频辐射的组合允许测量核自旋跃迁的四极系统，在纯磁实验相反，敏感的四极相互作用的绝对符号。这种符号的确定对于与计算的EFG张量进行比较是必不可少的。核四极矩和电场梯度张量之间的耦合是除了塞曼效应之外，核自旋I > +与环境之间最重要的相互作用。由于这种耦合强烈地依赖于核的电子环境，它是固体结构的敏感探针2，并且通过其对自旋弛豫的影响，也是运动过程的敏感探针。因此，核四极耦合张量的测定在晶体、粉末或非晶材料的磁共振研究中常常是一个重要的工具。测量值与理论计算数据的比较可以作为电子结构计算的检查或作为测量原子极化率的工具。3确定四极耦合常数的主要实验工具是高磁场4中的核磁共振（NMR）及其低场相对的核四极共振（NQR）。这些方法可以提供非常精确的四极耦合常数的大小数据，但是，它们对它的符号不敏感;只要核自旋系统的高温近似是有效的，四极耦合哈密顿量乘以-1对通过静态和振荡磁场的任何组合获得的观测到的磁共振谱没有影响。5因此，在有利的情况下，可以测量耦合常数相对于其他量的符号。作为一个例子，我们证明了Li在Li_3N中的两个不同位置的符号相反，但绝对符号仍然不一致
The interaction between the quadrupole moment of nuclear spins I > + with the electric-field-gradient (EFG) tensor leads to a splitting of the energy of the nuclear spin states. We show how the combination of laser and radio-frequency irradiation allows measurements of nuclear spin transitions in quadrupolar systems that are, in contrast to purely magnetic experiments, sensitive to the absolute sign of the quadrupole interaction. This determination of the sign is essential for comparison with calculated EFG tensors. The coupling between the nuclear quadrupole moment and the electric-field-gradient tensor is, besides th e Zeeman effect, the most important interaction of nuclear spins I > + with their environment.’ Since this coupling depends strongly on the electronic environment of the nucleus, it is a sensitive probe for the structure of solids2 and, through its effect on spin relaxation, also of motional processes. Determination of the nuclear quadrupole coupling tensor has, therefore, often been an important tool in magnetic resonance investigations of crystalline, powdered, or amorphous materials. Comparison of the measured values with theoretically calculated data can serve as a check for electronic-structure calculations or as a tool for measuring atomic polarizabilities.3 The main experimental tool for the determination of quadrupole coupling constants is nuclear magnetic resonance (NMR) in high magnetic fields 4 and its low-field relative, nuclear quadrupole resonance (NQR). These methods can provide very precise data on the magnitude of the quadrupole coupling constants; however, they are insensitive to its sign; multiplication of the quadrupole coupling Hamiltonian with - 1 has no effect on the observed magnetic resonance spectrum obtained by any combination of static and oscillatory magnetic fields, as long as th e hightemperature approximation for the nuclear-spin system is valid.5 It is, therefore, necessary to reduce the spin temperature to T ’ In favorable cases, it is possible to measure the sign of the coupling constant relative to other quantities. As an example, it was shown that the two different sites of Li in Li3N have opposite signs;’ the absolute sign, however, is still un