{"title":"核对电子自旋回波包络调制","authors":"G. Jeschke","doi":"10.1016/j.jmro.2023.100094","DOIUrl":null,"url":null,"abstract":"<div><p>The interaction of electron spins with homonuclear spin pairs in their vicinity is one of the dominating mechanisms of electron spin echo decay at low temperature and low concentration. Here, we study this mechanism using established concepts of electron spin echo envelope modulation (ESEEM). We obtain analytical expressions for the Hahn echo, the refocused echo, the stimulated echo, and Carr–Purcell pulse trains with small numbers of <span><math><mi>π</mi></math></span> pulses. Hahn echo decay is well approximated by the product of nuclear pair ESEEM functions. The same approximation can explain dependence of stimulated echo decay on the first interpulse delay and provides reasonable time scale estimates for decay of Carr–Purcell echos after an odd number of <span><math><mi>π</mi></math></span> pulses. Carr–Purcell echoes after an even number of <span><math><mi>π</mi></math></span> pulses are rather sensitive to correlations within larger nuclear spin clusters. Approximations improve for both odd and even numbers of <span><math><mi>π</mi></math></span> pulses by factorising the nuclear spin bath into disjoint clusters, provided that modulation due to pairs of spins belonging to different clusters is considered in addition to cluster modulation. The analytical ESEEM expressions for the Hahn echo and the Carr–Purcell echo after two <span><math><mi>π</mi></math></span> pulses have the same mathematical form as the filter functions of these sequences of spin noise spectroscopy. This coincidence provides a computationally very efficient way of predicting Hahn echo decay induced by homonuclear spin pairs. The analytical pair product approximation predicts the previously observed (Bahrenberg et al., 2021) increase of the refocused echo amplitude when one refocusing time is incremented and other one is fixed but longer. In contrast, the spin-noise concept fails to predict this effect.</p></div>","PeriodicalId":365,"journal":{"name":"Journal of Magnetic Resonance Open","volume":"14 ","pages":"Article 100094"},"PeriodicalIF":2.6240,"publicationDate":"2023-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"3","resultStr":"{\"title\":\"Nuclear pair electron spin echo envelope modulation\",\"authors\":\"G. Jeschke\",\"doi\":\"10.1016/j.jmro.2023.100094\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>The interaction of electron spins with homonuclear spin pairs in their vicinity is one of the dominating mechanisms of electron spin echo decay at low temperature and low concentration. Here, we study this mechanism using established concepts of electron spin echo envelope modulation (ESEEM). We obtain analytical expressions for the Hahn echo, the refocused echo, the stimulated echo, and Carr–Purcell pulse trains with small numbers of <span><math><mi>π</mi></math></span> pulses. Hahn echo decay is well approximated by the product of nuclear pair ESEEM functions. The same approximation can explain dependence of stimulated echo decay on the first interpulse delay and provides reasonable time scale estimates for decay of Carr–Purcell echos after an odd number of <span><math><mi>π</mi></math></span> pulses. Carr–Purcell echoes after an even number of <span><math><mi>π</mi></math></span> pulses are rather sensitive to correlations within larger nuclear spin clusters. Approximations improve for both odd and even numbers of <span><math><mi>π</mi></math></span> pulses by factorising the nuclear spin bath into disjoint clusters, provided that modulation due to pairs of spins belonging to different clusters is considered in addition to cluster modulation. The analytical ESEEM expressions for the Hahn echo and the Carr–Purcell echo after two <span><math><mi>π</mi></math></span> pulses have the same mathematical form as the filter functions of these sequences of spin noise spectroscopy. This coincidence provides a computationally very efficient way of predicting Hahn echo decay induced by homonuclear spin pairs. The analytical pair product approximation predicts the previously observed (Bahrenberg et al., 2021) increase of the refocused echo amplitude when one refocusing time is incremented and other one is fixed but longer. 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引用次数: 3
摘要
电子自旋与周围同核自旋对的相互作用是低温低浓度下电子自旋回波衰减的主要机制之一。在这里,我们使用电子自旋回波包络调制(ESEEM)的既定概念来研究这种机制。得到了Hahn回波、重聚焦回波、受激回波和具有少量π脉冲的Carr-Purcell脉冲序列的解析表达式。核对ESEEM函数的乘积很好地近似于Hahn回波衰减。同样的近似可以解释受激回波衰减对第一脉冲间延迟的依赖,并为奇数π脉冲后的Carr-Purcell回波衰减提供合理的时间尺度估计。偶数π脉冲后的Carr-Purcell回波对较大核自旋团簇内的相关性相当敏感。通过将核自旋池分解成不相交的团簇,近似改进了奇数和偶数π脉冲,前提是除了团簇调制外,还考虑了属于不同团簇的自旋对的调制。两个π脉冲后Hahn回波和Carr-Purcell回波的解析ESEEM表达式与这些自旋噪声光谱序列的滤波函数具有相同的数学形式。这种巧合提供了一种计算上非常有效的方法来预测由同核自旋对引起的哈恩回声衰减。解析对积近似预测了先前观察到的(Bahrenberg et al., 2021),当一个重聚焦时间增加,另一个重聚焦时间固定但更长时,重聚焦回波振幅会增加。相比之下,自旋噪声的概念无法预测这种效应。
Nuclear pair electron spin echo envelope modulation
The interaction of electron spins with homonuclear spin pairs in their vicinity is one of the dominating mechanisms of electron spin echo decay at low temperature and low concentration. Here, we study this mechanism using established concepts of electron spin echo envelope modulation (ESEEM). We obtain analytical expressions for the Hahn echo, the refocused echo, the stimulated echo, and Carr–Purcell pulse trains with small numbers of pulses. Hahn echo decay is well approximated by the product of nuclear pair ESEEM functions. The same approximation can explain dependence of stimulated echo decay on the first interpulse delay and provides reasonable time scale estimates for decay of Carr–Purcell echos after an odd number of pulses. Carr–Purcell echoes after an even number of pulses are rather sensitive to correlations within larger nuclear spin clusters. Approximations improve for both odd and even numbers of pulses by factorising the nuclear spin bath into disjoint clusters, provided that modulation due to pairs of spins belonging to different clusters is considered in addition to cluster modulation. The analytical ESEEM expressions for the Hahn echo and the Carr–Purcell echo after two pulses have the same mathematical form as the filter functions of these sequences of spin noise spectroscopy. This coincidence provides a computationally very efficient way of predicting Hahn echo decay induced by homonuclear spin pairs. The analytical pair product approximation predicts the previously observed (Bahrenberg et al., 2021) increase of the refocused echo amplitude when one refocusing time is incremented and other one is fixed but longer. In contrast, the spin-noise concept fails to predict this effect.