High-Frequency EPR, ESEEM and ENDOR Studies of Paramagnetic Canters in Single-Crystalline Materials

Abstract

In this contribution an account is given of Electron Paramagnetic Resonance (EPR), Electron Spin Echo Envelope Modulation (ESEEM) and Electron Nuclear Double Resonance (ENDOR) studies at 95 GHz on paramagnetic centers in two types of very different single-crystalline materials. The first concerns a study of the electronic and geometric structure of acceptors in single crystals of the wide-band-gap semiconductor SiC. The second concerns a study of the paramagnetic centers in single crystals of copper proteins. The results demonstrate two advantages of working at this high frequency. First it is possible to investigate single crystals that are limited in their linear dimensions to a few tenths of mm. Secondly, owing to the high spectral resolution in EPR as well as in ENDOR spectroscopy it is possible to separate the EPR signals of sites with very small differences in their g-tensor and to resolve the ENDOR signals of different nuclei. These two aspects allow the assignment of the EPR signals to specific sites in the single crystal and to determine the spatial distribution of the electronic wave function of the paramagnetic centre.