Investigations on the establishment and applications of pulsed ENDOR

在本研究项目的最后一个学期，对迄今为止获得的主要结果进行了广泛的研究，以完成本研究项目，特别是两种脉冲ENDOR方法的创新发展及其特点。我们采用了两种不同的方法，一种是从tm模腔开始的，这是CW-ENDOR或TRIPLE光谱的标准方法，另一种是从te模腔开始的，这是广泛用于脉冲ESR光谱的方法。首先，我们分析了这些空腔的特性，并研究了如何将它们修改为脉冲ENDOR实验。结果表明，与te模腔相比，tm模腔具有更高的ENDOR效应。但由于微波脉冲功率较弱，其信噪比较低。双脉冲或三脉冲序列（Davis或Mims ENDOR）后的微弱自旋回波是影响其广泛应用的严重缺陷之一。另一方面，在针对脉冲ENDOR进行改进的te模腔中，预期会产生较强的自旋回波，从而导致产生多少ENDOR效应的问题。尽管回波高度较弱，但传统脉冲ENDOR光谱的光谱分辨率和信噪比都很好。te模腔的关键是在样品周围实现高射频功率。我们的想法之一是使用Z-coil系统，这在这个项目中是第一次体验。另一个想法是提出90度旋转腔通常te模式，这也是第一次设计和制造。最后指出了今后脉冲ENDOR光谱的完善需要解决的问题和不足。由于研究项目时间较短，经费有限，应用研究不能令人满意。

In the last term of this research project, the main results obtained so far were examined extensively to conclude this research project, especially innovative developments of two pulsed ENDOR methods and their characteristics. We pursued two different approaches, one starting from TM-mode cavity, which is a standard method for CW-ENDOR or TRIPLE spectroscopy, and one from TE-mode cavity, which is widely used for pulsed ESR spectroscopy. First we analyzed characteristics of these cavities, and examined how they could be modified to pulsed ENDOR experiments.It was established that an ENDOR cavity modified from TM-mode exhibits high ENDOR effect compared to the cavity from TE-mode. But it gave low S/N ratio, because of weak microwave pulse power. The weak spin echo after two- or three-pulse sequence(Davis or Mims ENDOR)is one of the severe drawbacks for the applications in the wide variety of fields. In the TE-mode cavity modified for pulse ENDOR, on the other hand, strong spin echoes are expected so that it leads to the problem how much ENDOR effect results in. In spite of the weak echo height, spectrum resolution as well as S/N ratio were found excellent for conventional pulsed ENDOR spectroscopy. The important point for the TE-mode cavityis accomplishment of high radio frequency power around the samples. One of our ideas is employment of Z-coil system, wllich was first experienced in this project. Another idea is proposal of the 90-degree rotated cavity for usual TE-mode, which was also first designed and manufactured.Some deffects or problems which should be reloved in future were pointed out finally for complete establishment of the pulsed ENDOR spectroscopy. Applicable research could not be made satisfactorily partly due to short term of the research project and limited fund.