CIRCULAR DICHROISM ESR

这个子项目是利用资源的许多研究子项目之一。 由NIH/NCRR资助的中心拨款提供。对子项目的主要支持 子项目的首席调查员可能是由其他来源提供的， 包括美国国立卫生研究院的其他来源。为子项目列出的总成本可能 表示该子项目使用的中心基础设施的估计数量， 不是由NCRR赠款提供给次级项目或次级项目工作人员的直接资金。 影响电子自旋共振波谱在化学和生物学中广泛应用的一个重要问题是磁场调制对S/N的限制。为了使信号最大化，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在20G以下，以防止样品过度加热。然而，许多HFHF-ESR线宽通常大于100G，因此开发场调制的替代方案是可取的。通常，为了具有可观测的信号，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(CD)光谱偏振仪中常见的技术的可能性，并将它们改装到HFHF-ESR光谱仪中，以在不使用磁场调制的情况下调制ESR共振。我们称这项技术为CD-ESR。这项技术依赖于在给定的参考频率上交替使用两个相反的圆偏振光束来照明ESR样品。在ESR样品中存在圆偏振态之一的优先吸收，这满足所谓的调制转移原理。最近的努力集中在开发一种具有两个圆偏振态的相等幅度的偏振调制器，以便最大限度地减少仪器伪影。我们最近对我们的高频ESR光谱仪进行的升级将促进这项技术的实施。我们目前还在研究对170 GHz和240 GHz的CW源进行改装的可能性，以提供一种坚固可靠的方法来实现必要的偏振调制。我们正在实现的修改后的反射桥足够灵活，允许我们以一种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.