CIRCULAR DICHROISM ESR

该子项目是利用资源的众多研究子项目之一 由 NIH/NCRR 资助的中心拨款提供。子项目的主要支持 并且子项目的主要研究者可能是由其他来源提供的， 包括其他 NIH 来源。 子项目可能列出的总成本 代表子项目使用的中心基础设施的估计数量， NCRR 赠款不直接向子项目或子项目工作人员提供资金。 影响 ESR 光谱在化学和生物学中广泛问题的适用性的重要问题之一是磁场调制对信噪比的限制。 为了最大化信号，需要与线宽相当的调制幅度。对于高场/高频 ESR (HFHF-ESR)，洛伦兹力将场调制幅度限制为小于 20G，以防止样品过度加热。 然而，许多 HFHF-ESR 线宽通常大于 100G，因此需要开发场调制的替代方案。 一般来说，为了获得可观测的信号，通常需要某种形式的信号编码。 我们目前正在探索使用光学圆二色性 (CD) 分光偏振计中常见技术的可能性，并将其应用于 HFHF-ESR 分光计，以在不使用磁场调制的情况下调制 ESR 共振。我们将该技术称为 CD-ESR。 该技术依赖于在给定参考频率下用两束相反的圆偏振光束交替照射 ESR 样品。 ESR 样品内存在满足所谓的调制传递原理的圆偏振态之一的优先吸收。 最近的努力集中在开发两种圆偏振态振幅相等的偏振调制器，以最大限度地减少仪器伪影。 我们最近对 HFHF ESR 光谱仪进行的升级将有助于这项技术的实施。 我们目前还在研究是否可以修改我们的 170 和 240GHz 连续波源，以提供一种坚固、可靠的方法来实现必要的偏振调制。 我们正在实施的修改后的反射桥足够灵活，允许我们以直接的方式测试这些想法。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. One of the important issues that affects the applicability of ESR spectroscopy to a wide range of problems in chemistry and biology is the constraint of magnetic field modulation on the S/N. In order to maximize the signal, one needs modulation amplitudes that are comparable to the linewidth. For high-field/high-frequency-ESR (HFHF-ESR), Lorentz forces limit field modulation amplitudes to less than 20G in order to prevent excessive sample heating. However, many HFHF-ESR linewidths are often greater than 100G, and so it is desirable to develop alternatives to field modulation. In general, some form of signal coding is usually necessary to have an observable signal. We are currently exploring the possibility of using techniques that are common in optical circular dichroism (CD) spectropolarimeters and adapting them to a HFHF-ESR spectrometer to modulate the ESR resonance without using magnetic field modulation. We call the technique CD-ESR. The technique relies on illuminating the ESR sample with two oppositely circularly polarized beams in alternation at a given reference frequency. There is preferential absorption within the ESR sample of one of the circular polarization states which satisfies the so-called Transfer of Modulation principle. Recent efforts have focused on developing a polarization modulator with equal amplitudes of both circular polarization states in order to minimize instrumental artifacts. The recent upgrades that we have made to our HFHF ESR spectrometers will facilitate the implementation of this technique. We are also currently investigating the possibility that our cw sources at 170 and 240GHz may be modified to provide a rugged, reliable means for achieving the necessary polarization modulation. The modified reflection bridge we are implementing is sufficiently flexible to allow for us to test these ideas in a straightforward way.