Dynamic nuclear polarisation via the integrated solid effect I: theory
Dynamic nuclear polarisation via the integrated solid effect I: theory
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DOI：
10.1080/00268976.2013.861936
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发表时间：
2014-01-01
影响因子：
1.7
通讯作者：
Wenckebach, W. Th
中科院分区：
文献类型：
--
作者：
Henstra, A.;Wenckebach, W. Th
在称为动态核极化（DNP）的超极化方法中，将少量不成对电子自旋添加到含有核自旋的样品中，并且这些不成对电子自旋的极化通过微波场转移到核自旋。传统的DNP使用弱连续波(CW)微波场，因此可以使用微扰方法来计算偏振传输。通过使用强脉冲微波场的集成固体效应 (ISE)，可以获得更快的电子自旋极化转移。与通过电子自旋锁定的核取向一样，极化转移是相干的，类似于核自旋之间的相干转移。本文提出了计算这种偏振转移的理论方法。ISE 已成功用于从短寿命光激发三重态到分子晶体中周围核自旋的快速偏振转移。这些三重态在光激发过程中强烈排列，不需要传统 DNP 中极化电子自旋所需的低温和强磁场。在接下来的论文中，将该理论应用于萘-h(8)掺杂并五苯-d(14)的体系中，该体系提供了光激发三重态，并与实验结果进行了比较。
In the hyperpolarisation method known as dynamic nuclear polarisation (DNP), a small amount of unpaired electron spins is added to the sample containing the nuclear spins and the polarisation of these unpaired electron spins is transferred to the nuclear spins by means of a microwave field. Traditional DNP uses weak continuous wave (CW) microwave fields, so perturbation methods can be used to calculate the polarisation transfer. A much faster transfer of the electron spin polarisation is obtained with the integrated solid effect (ISE) which uses strong pulsed microwave fields. As in nuclear orientation via electron spin locking, the polarisation transfer is coherent, similar to the coherence transfer between nuclear spins. This paper presents a theoretical approach to calculate this polarisation transfer.ISE is successfully used for a fast polarisation transfer from short-lived photo-excited triplet states to the surrounding nuclear spins in molecular crystals. These triplet states are strongly aligned in the photo-excitation process and do not require the low temperatures and strong magnetic fields needed to polarise the electron spins in traditional DNP. In the following paper, the theory is applied to the system naphthalene-h(8) doped with pentacene-d(14) which provides the photo-excited triplet states, and compared with experimental results.