Physics Department, Natural and Exact Science Faculty, Northeastern University of Argentina, Corrientes, Argentina.
J Chem Phys. 2012 Jun 14;136(22):224110. doi: 10.1063/1.4729253.
We present here a systematic study about the influence of the size and type of nuclear charge-distribution models (Gaussian and point-like) on the NMR spectroscopic parameters, the nuclear magnetic shielding σ and the indirect nuclear spin J-coupling. We found that relativistic effects largely enhance the nuclear charge-distribution effects (NChDE) on those parameters being them quite sensitive to the nuclear model adopted for calculations. Results for two rare gas atoms (Kr, Rn) and few molecular systems like HX, (X = Br, I, At), CH(4), SnH(4), SnIH(3), SnI(2)H(2), and PbIH(3) are presented. J-couplings are more sensitive than shieldings in both, relativistic and non-relativistic (NR) regimes. The highest effect (close to 11% of variation in relativistic calculations with that two different nuclear models) is observed for J(Pb-I) in PbIH(3). A similar effect is found for J(Pb-H) in the same molecule, close to 9%. The NChDE for σ(Sn) in SnI(4-n)H(n) with n = 1, 2 is as large as few ppm (between 3 and 8.56 ppm). For J(Sn-H) in this set of molecules, it goes from 37 Hz for SnH(4) to 54 Hz for SnI(2)H(2). Furthermore, we found that the vicinal NChDE is very small though not zero. For (1)J(Sn-H) in SnIH(3), the NChDE of iodine is close to 2 Hz (0.1%). We also studied the NChDE on the ground state electronic energies of atoms and molecules. We found that these effects are only important within the relativistic regime but not within the NR one. They are in good agreement with previous works.
我们在这里呈现了一项关于核电荷分布模型（高斯型和点状）的大小和类型对 NMR 光谱参数、核磁屏蔽σ和间接核自旋 J 耦合的影响的系统研究。我们发现，相对论效应对这些参数的核电荷分布效应（NChDE）有很大的增强作用，而且这些参数对计算中采用的核模型非常敏感。我们给出了两个稀有气体原子（Kr、Rn）和几个分子体系（如 HX，X=Br、I、At，CH4，SnH4，SnIH3，SnI2H2，PbIH3）的结果。在相对论和非相对论（NR）两种情况下，J 耦合比屏蔽更敏感。在 PbIH3 中，J（Pb-I）在相对论计算中与两个不同的核模型的变化接近 11%，这是观察到的最高效应。在同一分子中，J（Pb-H）也存在类似的效应，接近 9%。在 SnI4-nHn 中（n=1，2），Sn 核的σ（Sn）的 NChDE 高达几个 ppm（3 到 8.56 ppm 之间）。对于这组分子中的 J（Sn-H），它从 SnH4 的 37 Hz 增加到 SnI2H2 的 54 Hz。此外，我们发现尽管不为零，但邻位 NChDE 非常小。对于 SnIH3 中的 1J（Sn-H），碘的 NChDE 接近 2 Hz（0.1%）。我们还研究了原子和分子的基态电子能量的 NChDE。我们发现这些效应仅在相对论范围内重要，而在非相对论范围内不重要。它们与以前的工作非常吻合。
