Wideband frequency-swept excitation in pulsed EPR spectroscopy
Wideband frequency-swept excitation in pulsed EPR spectroscopy
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DOI：
10.1016/j.jmr.2017.01.004
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发表时间：
2017-07-01
影响因子：
2.2
通讯作者：
Jeschke, Gunnar
中科院分区：
文献类型：
--
作者：
Doll, Andrin;Jeschke, Gunnar
用单色矩形脉冲激发电子自旋的带宽被限制为小于大多数有机自由基的光谱宽度并且远小于过渡和稀土金属离子的光谱宽度。对于频率扫描脉冲，先前已经获得了高达800 MHz的带宽，用于在约9.6 GHz的频率下激发和检测自旋包，并且在约34 GHz的频率下的极化转移实验中获得了高达2.5 GHz的带宽。其余的限制，主要是由于谐振器带宽和脉冲长度的限制进行了讨论。状态空间旋转的翻转角通常可以通过Landau-Zener-Stiickelberg-Majorana表达式从临界绝热性计算出来。对于双曲正割脉冲，Demkov-Kunike模型描述了扫描范围内和扫描范围外的自旋包的激发。在扫描范围内，布洛赫-西格特相移与临界绝热度成正比，达到非常好的近似。由于翻转角和相干相位都依赖于临界绝热性，因此使用提供这种与偏移无关的绝热性的振幅和频率调制函数对是有利的。谐振器响应函数的补偿应恢复与偏移无关的绝热性。尽管共振偏移和布洛赫-西格特相位可以在一定的脉冲长度比下重新聚焦，但耦合自旋系统中的相位色散通常不能重新聚焦。基于自旋动力学产生的带宽限制，要求推导出一个光谱仪，实现精确的自旋控制在宽带。讨论了这种谱仪的设计和EPR实验的硬件表征。(C)2017爱思唯尔公司All rights reserved.
Excitation of electron spins with monochromatic rectangular pulses is limited to bandwidths that are smaller than the spectral widths of most organic radicals and much smaller than the spectral widths of transition and rare earth metal ions. With frequency-swept pulses, bandwidths of up to 800 MHz have previously been attained for excitation and detection of spin packets at frequencies of about 9.6 GHz and bandwidths of up to 2.5 GHz in a polarization transfer experiment at frequencies of about 34 GHz. The remaining limitations, mainly due to resonator bandwidth and due to pulse length restrictions are discussed. Flip angles for state-space rotations on passage of a transition can generally be computed from the critical adiabaticity by the Landau-Zener-Stiickelberg-Majorana expression. For hyperbolic secant pulses, the Demkov-Kunike model describes excitation for spin packets within and outside the sweep range. Well within the sweep range, the Bloch-Siegert phase shift is proportional to critical adiabaticity to a very good approximation. Because of the dependence of both flip angle and coherence phase on critical adiabaticity, it is advantageous to use pairs of amplitude and frequency modulation functions that provide such offset-independent adiabaticity. Compensation for the resonator response function should restore offset-independent adiabaticity. Whereas resonance offsets and Bloch-Siegert phase can be refocused at certain pulse length ratios, phase dispersion in coupled spin systems cannot generally be refocused. Based on the bandwidth limitations that arise from spin dynamics, requirements are derived for a spectrometer that achieves precise spin control over wide bands. The design of such a spectrometer and hardware characterization by EPR experiments are discussed. (C) 2017 Elsevier Inc. All rights reserved.