Carravetta Marina, Levitt Malcolm H
Chemistry Department, Southampton University, SO17 1BJ Southampton, United Kingdom.
J Chem Phys. 2005 Jun 1;122(21):214505. doi: 10.1063/1.1893983.
We have recently demonstrated the existence of exceptionally long-lived nuclear spin states in solution-state nuclear magnetic resonance. The lifetime of nuclear spin singlet states in systems containing coupled pairs of spins-12 may exceed the conventional relaxation time constant T1 by more than an order of magnitude. These long lifetimes may be observed if the long-lived singlet states are prevented from mixing with rapidly relaxing triplet states. In this paper we provide the detailed theory of an experiment which uses magnetic field cycling to observe slow singlet relaxation. An approximate expression is given for the magnetic field dependence of the singlet relaxation rate constant, using a model of intramolecular dipole-dipole couplings and fluctuating external random fields.
我们最近在溶液态核磁共振中证实了超长寿命核自旋态的存在。在含有自旋为1/2的耦合对的体系中，核自旋单重态的寿命可能比传统弛豫时间常数T1超出一个多数量级。如果能防止长寿命单重态与快速弛豫的三重态混合，就可以观察到这些长寿命现象。在本文中，我们给出了一个利用磁场循环来观测缓慢单重态弛豫的实验的详细理论。利用分子内偶极-偶极耦合和波动的外部随机场模型，给出了单重态弛豫速率常数对磁场依赖性的近似表达式。
