Electron tunneling in lithium-ammonia solutions probed by frequency-dependent electron spin relaxation studies.
Electron tunneling in lithium-ammonia solutions probed by frequency-dependent electron spin relaxation studies.
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通过频率相关的电子自旋弛豫研究探测锂氨溶液中的电子隧道效应。
DOI：
10.1021/ja212015b
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发表时间：
2012
影响因子：
15
通讯作者：
Edwards,PeterP
中科院分区：
文献类型：
--
作者：
Maeda,Kiminori;Lodge,MatthewTJ;Harmer,Jeffrey;Freed,JackH;Edwards,PeterP
用脉冲电子顺磁共振（EPR）谱在X波段（9.7 GHz）和W波段（94 GHz）研究了锂-氨稀溶液中过量或溶剂化电子的电子转移或量子隧穿动力学。电子自旋-晶格（T1）和自旋-自旋（T2）弛豫数据表明这些溶液中溶剂化电子的极快转移或量子隧穿速率，其用于调制超精细结构。与氨分子溶剂化壳层中氮核的（费米接触）相互作用围绕局部的，这些溶液中溶剂化电子的供体和受体状态是在转移或隧穿过程之前和之后发现的初始和最终电子溶剂化位点。为了解释和模拟我们的电子自旋弛豫数据从两个观察EPR频率需要考虑的多指数相关函数。在230-290 K温度范围内，我们通过氮费米接触相互作用的相关时间监测的电子转移或隧穿过程在我们最稀的锂氨溶液中的时间尺度为（1-10）× 10- 12 s。两种类型的电子-溶剂相互作用机制，提出了我们的实验结果。主要的电子自旋弛豫机制由电子隧穿过程产生，该电子隧穿过程的特征在于可变的供体-受体距离或范围（与这种快速波动的液体结构一致），其中最终接受转移电子的溶剂壳层由液体中的天然空穴或类Bjerrum缺陷空位中和周围的液体结构的随机热波动形成。在隧穿电子的转移和捕获之后，进一步的溶剂笼弛豫（时间尺度为10- 13 s）对电子自旋弛豫时间的贡献很小。这项调查说明了多频EPR测量的巨大潜力，询问超快电子转移或量子隧穿过程在液体中的微观性质和动力学。我们的研究结果也影响了普遍的问题的主机溶剂（或主机矩阵，如半导体）在介导的远程电子转移过程中的作用，我们讨论了我们的结果与一系列其他材料和系统表现出的电子转移现象的影响。
Electron transfer or quantum tunneling dynamics for excess or solvated electrons in dilute lithium–ammonia solutions have been studied by pulse electron paramagnetic resonance (EPR) spectroscopy at both X- (9.7 GHz) and W-band (94 GHz) frequencies. The electron spin–lattice (T1) and spin–spin (T2) relaxation data indicate an extremely fast transfer or quantum tunneling rate of the solvated electron in these solutions which serves to modulate the hyperfine (Fermi-contact) interaction with nitrogen nuclei in the solvation shells of ammonia molecules surrounding the localized, solvated electron. The donor and acceptor states of the solvated electron in these solutions are the initial and final electron solvation sites found before, and after, the transfer or tunneling process. To interpret and model our electron spin relaxation data from the two observation EPR frequencies requires a consideration of a multiexponential correlation function. The electron transfer or tunneling process that we monitor through the correlation time of the nitrogen Fermi-contact interaction has a time scale of (1–10) × 10–12s over a temperature range 230–290 K in our most dilute solution of lithium in ammonia. Two types of electron–solvent interaction mechanisms are proposed to account for our experimental findings. The dominant electron spin relaxation mechanism results from an electron tunneling process characterized by a variable donor–acceptor distance or range (consistent with such a rapidly fluctuating liquid structure) in which the solvent shell that ultimately accepts the transferring electron is formed from random, thermal fluctuations of the liquid structure in, and around, a natural hole or Bjerrum-like defect vacancy in the liquid. Following transfer and capture of the tunneling electron, further solvent-cage relaxation with a time scale of ∼10–13s results in a minor contribution to the electron spin relaxation times. This investigation illustrates the great potential of multifrequency EPR measurements to interrogate the microscopic nature and dynamics of ultrafast electron transfer or quantum-tunneling processes in liquids. Our results also impact on the universal issue of the role of a host solvent (or host matrix, e.g. a semiconductor) in mediating long-range electron transfer processes and we discuss the implications of our results with a range of other materials and systems exhibiting the phenomenon of electron transfer.
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DOI：
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期刊：
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DOI：
10.1021/j150661a003
发表时间：
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期刊：
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影响因子：
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