CIRCULAR DICHROISM ESR

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 影响ESR波谱在化学和生物学中广泛应用的重要问题之一是磁场调制对S/N的约束。 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在20 G以下，以防止样品过度加热。 然而，许多HFHF-ESR线宽通常大于100 G，因此期望开发场调制的替代方案。 一般来说，某种形式的信号编码通常是必要的，以获得可观察的信号。 我们目前正在探索使用的技术是常见的光学圆二色性（CD）分光光度计和调整它们的HFHF-ESR光谱仪调制ESR共振，而不使用磁场调制的可能性。我们称之为CD-ESR技术。 该技术依赖于以给定的参考频率交替地用两个相反的圆偏振光束照射ESR样品。 在ESR样品内存在满足所谓的调制转移原理的圆偏振态之一的优先吸收。 最近的努力集中在开发具有相等幅度的两个圆偏振态的偏振调制器，以便最小化仪器伪影。 我们最近对HFHF ESR谱仪进行的升级将促进这项技术的实施。 我们目前还在研究我们在170和240 GHz的连续波源可能被修改，以提供一个坚固，可靠的手段，实现必要的偏振调制的可能性。 我们正在实现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. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. 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.