Faculty of Chemistry, University of Warsaw, Warszawa, Poland.
J Phys Chem A. 2012 Dec 6;116(48):11896-904. doi: 10.1021/jp309820v. Epub 2012 Nov 19.
We present the results of gas-phase NMR measurements designed to yield a new experimental value for the absolute (1)H magnetic shielding for an isolated hydrogen molecule and its deuterium isotopomers. The results are based on the original method of direct shielding measurements (Jackowski et al., 2010) and the density dependence of (1)H, (2)H, and (3)He NMR frequencies for molecular hydrogen and atomic helium-3. The absolute isotropic magnetic shielding measured for molecular hydrogen, σ(0)(H(2)), is 26.293(5) ppm at 300 K, within experimental error of previous measurements based on spin-rotation data and quantum chemistry computations, 26.289(2) ppm (Sundholm and Gauss, 1997), and recent ab initio calculations. We also report isotope effects in shielding for H(2), HD, and D(2) molecules that are consistent with theoretical predictions. In addition, gas-phase (1)H chemical shifts extrapolated to zero density have been measured for numerous small molecules. Our results yield precise absolute shielding data that will be useful in establishing benchmark computational chemistry methods for calculating rovibrational averaged magnetic shielding.
我们呈现了气相 NMR 测量的结果，旨在为孤立氢分子及其氘同位素的绝对（1）H 磁屏蔽提供新的实验值。结果基于直接屏蔽测量的原始方法（Jackowski 等人，2010 年）以及分子氢和氦-3 原子的（1）H、（2）H 和（3）He NMR 频率对密度的依赖性。在 300 K 下测量的分子氢的绝对各向同性磁屏蔽，σ（0）（H（2））为 26.293（5）ppm，在实验误差范围内与先前基于自旋旋转数据和量子化学计算的测量值 26.289（2）ppm（Sundholm 和 Gauss，1997 年）以及最近的从头算计算值一致。我们还报告了 H（2）、HD 和 D（2）分子屏蔽中的同位素效应，这些效应与理论预测一致。此外，还测量了许多小分子在零密度下的气相（1）H 化学位移。我们的结果提供了精确的绝对屏蔽数据，这对于建立用于计算转动振动平均磁屏蔽的基准计算化学方法将非常有用。
