Aucar I Agustín, Gomez Sergio S, Giribet Claudia G, Aucar Gustavo A
Instituto de Modelado e Innovación Tecnológica, CONICET, and Departamento de Física, FCENA-UNNE, Avda. Libertad 5460, W3404AAS Corrientes, Argentina.
Instituto de Fı́sica de Buenos Aires, CONICET, and Departamento de Fı́sica, FCEN-UBA, Ciudad Universitaria, C1428EGA Buenos Aires, Argentina.
J Phys Chem Lett. 2016 Dec 15;7(24):5188-5192. doi: 10.1021/acs.jpclett.6b02361. Epub 2016 Dec 2.
The broadly accepted procedure to obtain the experimental absolute scale of NMR magnetic shieldings, σ, is well-known for nonheavy atom-containing molecules. It was uncovered more than 40 years ago by the works of Ramsey and Flygare. They found a quite accurate relationship among σ and the nuclear spin-rotation constants. Its relativistic extension was very recently proposed, although it has an intrinsic weakness because a new SO-S two-component term needs to be considered. We show how to overcome this problem. We found that (ν - ν) generalizes the SO-S term, where ν = ⟨⟨[((r - r) × α)/(|r - r|)]; S⟩⟩, r - r is the electron position with respect to the position of nucleus Y, and S is the four-component total electron spin. When including this new term, one finds that the best of our relativistic Flygare-like models fits quite well with the results of the most accurate method available at the moment. We also show that the difference among the parallel component of σ(Xe) in XeF and σ(Xe) of the free atom is almost completely described by that new term.
获得核磁共振磁屏蔽实验绝对标度σ的广泛接受的程序，对于不含重原子的分子是众所周知的。它是40多年前由拉姆齐（Ramsey）和弗莱加雷（Flygare）的工作发现的。他们发现了σ与核自旋 - 旋转常数之间相当精确的关系。其相对论扩展最近才被提出，尽管它有一个内在的弱点，因为需要考虑一个新的SO - S二分量项。我们展示了如何克服这个问题。我们发现(ν - ν)概括了SO - S项，其中ν = ⟨⟨[((r - r) × α)/(|r - r|)]; S⟩⟩，r - r是相对于原子核Y位置的电子位置，S是四分量总电子自旋。当包含这个新项时，可以发现我们最好的类弗莱加雷相对论模型与目前可用的最精确方法的结果拟合得相当好。我们还表明，XeF中σ(Xe)的平行分量与自由原子的σ(Xe)之间的差异几乎完全由那个新项描述。
