Mitrikas George, Prokopiou Georgia
Institute of Nanoscience and Nanotechnology, NCSR Demokritos, 15310 Athens, Greece.
Institute of Nanoscience and Nanotechnology, NCSR Demokritos, 15310 Athens, Greece.
J Magn Reson. 2015 May;254:75-85. doi: 10.1016/j.jmr.2015.03.002. Epub 2015 Mar 12.
We present a new way to increase the modulation amplitude of electron spin echo envelope modulation (ESEEM) experiments that are based on electron spin coherence. The method uses a train of N refocusing π-pulses where each one of them redistributes the electron spin coherence among allowed and forbidden EPR transitions. This in turn leads to a significant enhancement of the ESEEM effect, depending on the strength of the hyperfine interaction and the number of applied pulses, N. We derive analytical expressions for a general two-dimensional (2D) scheme which is based on the refocused primary echo and we explore the expected modulation enhancement of various correlation peaks as a function of k (modulation depth parameter) and N. In addition, we inspect two different one-dimensional (1D) versions of the method, namely the Carr-Purcell-Meiboom-Gill (CPMG) sequence occurring for t1=t2, and an extension of the primary echo sequence occurring for t2=0. Our study shows that these methods are particularly useful for detecting weak hyperfine couplings of magnetic nuclei having small gn factors and low natural abundances like (13)C and (29)Si. The theoretically predicted features are confirmed by experiments in disordered spin systems.
我们提出了一种新方法，用于增加基于电子自旋相干性的电子自旋回波包络调制（ESEEM）实验的调制幅度。该方法使用一串N个重聚焦π脉冲，其中每个脉冲都会在允许和禁止的电子顺磁共振（EPR）跃迁之间重新分配电子自旋相干性。这反过来又会导致ESEEM效应显著增强，这取决于超精细相互作用的强度和所施加脉冲的数量N。我们推导了基于重聚焦初级回波的一般二维（2D）方案的解析表达式，并探讨了各种相关峰的预期调制增强作为k（调制深度参数）和N的函数。此外，我们研究了该方法的两种不同的一维（1D）版本，即t1 = t2时出现的Carr-Purcell-Meiboom-Gill（CPMG）序列，以及t2 = 0时出现的初级回波序列的扩展。我们的研究表明，这些方法对于检测具有小gn因子和低天然丰度的磁性核（如¹³C和²⁹Si）的弱超精细耦合特别有用。理论预测的特征在无序自旋系统的实验中得到了证实。
