液体NMR中平板间多量子相干受限扩散行为的有限差分模拟

Finite Difference Simulation of Restricted-Diffusion Behaviors of Multiple-Quantum Coherences Between Two Parallel Plates in Liquid NMR

将平板间单量子相干受限扩散理论表述推广到多量子相干,并结合积算符矩阵、Bloch方程和有限差分方法进行模拟.通过模拟找出平板间受限扩散信号衰减随平板间距变化的规律,并与实际体系比较.结果表明:平板间n量子相干的自旋回波信号衰减曲线与单量子类似,且其产生同样衍射图样所需的脉冲梯度场强度仅为单量子的1/|n|,可用于测量微小的平板间距.本文的模拟方法可进一步推广到复杂体系的研究.

To understand the properties of restricted diffusion of multiple-quantum coherences （MQCs） between two parallel plates, the restricted diffusion theory of singlequantum coherences （SQCs） was extended to MQCs. The method of finite difference was employed to simulate the NMR signal attenuation due to the restricted diffusion in combination with the product operator matrix and Bloch equations. The results show that, like SQCs, the MQC signal attenuation due to restricted diffusion gives diffraction-like pattern. However, the pulsed-field-gradient intensity required for MQCs to produce same diffraction-like pattern is only 1/｜n｜ of that for SQCs. The small distance between two arbitrary planes can be deduced when the relationship of signal attenuation due to diffusion with different inter-plane distance is obtained. The simulation method used herein can be further extended to study more complicated systems.