SINGLE CRYSTAL ROTATION FOR 250GHZ ESR

这个子项目是利用由NIH/NCRR资助的中心拨款提供的资源的许多研究子项目之一。子项目和调查员(PI)可能从另一个NIH来源获得了主要资金，因此可能会出现在其他CRISE条目中。列出的机构是针对中心的，而不一定是针对调查员的机构。在许多情况下，高场ESR谱在定向分辨率上比低场谱有相当大的提高。认识到这一点，我们现在已经成功地将我们的能力扩展到高场下Kramers和非Kramers过渡金属离子的单晶旋转研究。我们的设计受到了W波段单轴和多轴测角仪的影响。然而，我们在我们的设计中融入了许多功能，这些功能是专门为在低温下在法布里-普罗谐振器中操作而量身定做的。对单晶转动的多频率研究使人们能够更精确地确定自旋哈密顿量中与取向有关的项，如g矩阵、超精细矩阵和零场分裂(ZFS)张量。在足够高的场下，单晶的高场光谱具有比粉末光谱更窄的本征线宽，可以用来可信地指定对角线零位移项。在较低的场中，ZFS张量中的非对角项变得重要。这些信息，加上对ESR活性部分的仔细建模，可以用来获得重要的结构信息。具有大零点分裂的金属酶的单晶研究将特别受益于多频率方法。考虑到许多重要生物系统的低对称性或不完全对称性，开发一种能够在具有多轴能力的多频率光谱仪中平稳工作并且对于具有较短弛豫时间的系统在低温下高效工作的测角器是很重要的。我们目前使用的单轴测角仪的改进型，具有更高的精度，即将完成，并将作为开发高精度多轴测角仪的试验台。我们将把这种更高精度的测角仪集成到我们新开发的宽带电桥中，它具有更好的温度控制和更高的灵敏度，以促进对各种生物相关单晶体的研究。

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. High-field ESR spectra offer considerable improvements in orientational resolution over low field spectra, in many cases. Recognizing this, we have now successfully extended our capabilities to single-crystal rotation studies of Kramers and non-Kramers transition metal ions at high fields. Our design was influenced by single and multi-axis goniometers at W-band. However, we have incorporated a number of features into our design, which are specifically tailored to facilitate operation at low temperatures in a Fabry-P¿rot resonator. Multifrequency studies of single-crystal rotations allow one to more precisely determine the orientation-dependent terms in the spin-hamiltonian, such as the g-matrix, hyperfine-matrix and the zero-field splitting (ZFS) tensor. At sufficiently high fields, high-field spectra of single crystals with their narrower intrinsic linewidth compared to powder spectra may be used to assign the diagonal ZFS terms with confidence. At lower fields, the off-diagonal terms in the ZFS tensor become significant. This information, along with careful modeling of the ESR active moiety, can be used to obtain important structural information. Single-crystal studies of metalloenzymes with large ZFS splittings will particularly benefit from a multifrequency approach. Given the low or imperfect symmetry of many important biological systems, it is important to develop a goniometer that will work smoothly in a multi-frequency spectrometer with a multi-axis capability, as well as have efficient operation at low-temperatures for systems with short relaxation times. An improved version of the single-axis goniometer we have been using hitherto, featuring higher precision, is nearly completed and will serve as a test bed for developing a high precision multi-axis goniometer. We will incorporate this higher precision goniometer into our newly developed broadband bridge with improved temperature control and higher sensitivity to facilitate the study of a variety of biologically relevant single crystals.