Physikalisch-Technische Bundesanstalt (PTB), Berlin, Germany.
J Chem Phys. 2011 Aug 7;135(5):054201. doi: 10.1063/1.3623024.
In this study, we revisited nuclear magnetic relaxation of (1)H in water at very low Larmor frequencies that has been studied intensively in earlier years. We make use of the recently developed superconducting quantum interference device based ultra-low field NMR technique, which enables much easier access to the longitudinal spin-lattice relaxation time T(1) and the transversal spin-spin relaxation time T(2) below several kHz than traditional field cycling methods. Our data reproduce and complement the earlier results, in that they corroborate the finding of an exchange process with a correlation time of about 0.34 ms at room temperature which can be attributed to the migration of hydronium and hydroxyl ions in neutral water via hydrogen bridges. The corresponding relaxation process is driven by the interaction of the protons with (17)O and contributes to the T(1) and the T(2) relaxation rate by about 0.12 s(-1). In addition, we found evidence of a very slow exchange process at about 100 Hz that has hitherto not been reported.
在这项研究中，我们重新研究了早年曾被深入研究过的极低拉莫尔频率下（1）H 的核磁弛豫。我们利用最近开发的基于超导量子干涉装置的超低场 NMR 技术，与传统的场循环方法相比，该技术可以更容易地获得低于几 kHz 的纵向自旋晶格弛豫时间 T(1)和横向自旋-自旋弛豫时间 T(2)。我们的数据再现并补充了早期的结果，因为它们证实了在室温下存在一个交换过程的发现，其相关时间约为 0.34 ms，这可以归因于通过氢键在中性水中迁移的水合氢离子和氢氧根离子。相应的弛豫过程是由质子与（17）O 的相互作用驱动的，通过大约 0.12 s(-1)贡献于 T(1)和 T(2)弛豫率。此外，我们还发现了迄今尚未报道的约 100 Hz 的非常缓慢的交换过程的证据。
