A many-body analysis of the effects of the matrix protons and their diffusional motion on electron spin resonance line shapes and electron spin echoes
A many-body analysis of the effects of the matrix protons and their diffusional motion on electron spin resonance line shapes and electron spin echoes
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DOI：
10.1063/1.1382817
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发表时间：
2001-08-08
影响因子：
4.4
通讯作者：
Freed, JH
中科院分区：
文献类型：
--
作者：
Nevzorov, AA;Freed, JH
本文应用多自旋系统密度矩阵演化的处理方法，计算了自旋A与N个相同自旋B的熔池相互作用的磁共振信号。假设B自旋的旋磁比比A小得多(例如，前者是核自旋，I，而后者是电子自旋，S)。通过考虑存在B-B偶极相互作用时A自旋与所有B自旋的偶极耦合，解释了实验观察到的自旋-回波包络衰减对浓度和时间的二次依赖关系。结果表明，刚性极限下的自旋-回波包络衰变是由于A自旋与耦合自旋B的相干多体态通过核触发项I+/-I-/+相互作用而产生的，这在热力学极限中是一种耗散机制。这代表了一种比基于非相干版本的“自旋扩散”的简化模型更严格的分析，并且它导致了与实验很好的定量一致。此外，这种分析代表了对A自旋回波的调制和衰减的统一描述。对于使B自旋随机化的有限运动，还计算了A-B-N系统的自旋回波和线形。即使对于非常慢的运动(模拟为平移扩散)，也会产生一个有效的自旋-回波包络衰减机制，其重要性很容易超过相干机制。计算了由伪分子相互作用项SzI+/-引起的B自旋多量子跃迁引起的A自旋线形禁忌分量的强度分布。在刚性极限下，它的行为类似于泊松分布。(C)2001年美国物理研究所。
The method for treating the evolution of the density matrix developed in the accompanying paper for many-spin systems is applied here for calculating magnetic resonance signals of a spin A interacting with a bath of N identical spins B. Spins B are assumed to have much smaller gyromagnetic ratios than the spin A (e.g., the former are nuclear spins, I and the latter is an electron spin, S). The experimentally observed quadratic dependence of the spin-echo envelope decay on concentration and time is explained from considering the dipolar coupling of spin A to all the B spins in the presence of B-B dipolar interactions. It is shown that the spin-echo envelope decay in the rigid limit is due to the interaction of the A spin with the coherent many-body states of the coupled spins B via the nuclear flip-flop terms I+/-I-/+ which becomes a dissipative mechanism in the thermodynamic limit. This represents a more rigorous analysis than simplified models based on an incoherent version of "spin diffusion," and it leads to good quantitative agreement with experiment. Moreover, this analysis represents a unified description of both the modulation and decay of the A-spin echoes. Spin echoes and line shapes for the A-B-N systems are also calculated for finite motions which randomize the B spins. Even for very slow motions (modeled as translational diffusion) an effective mechanism for spin-echo envelope decay is generated, which readily overtakes the coherent mechanism in importance. The intensity distribution for the forbidden components in the A-spin line shape resulting from multiquantum transitions of the B spins caused by the pseudosecular interaction terms SzI+/-, is calculated. In the rigid limit it is found to behave like a Poisson distribution. (C) 2001 American Institute of Physics.