ENDOR in disordered solids

Single crystal ENDOR measurement is an informative but not always applicable method to identify paramagnetic species in solids. It is for instance difficult to obtain single crystals of biochemical materials. In other cases the paramagnetic species are intentionally trapped in a disordered matrix or in a frozen solution. The ENDOR lines are then usually broadened by the anisotropy of the magnetic couplings. Some data that a single crystal analysis can provide are difficult to extract from a powder sample. However, a considerable amount of information can often be obtained from ENDOR spectra of disordered systems. 

Applications of ENDOR spectroscopy to the study of radical cations in halo-carbon matrices have been reviewed [33]. Radicals on surfaces [34] and of paramagnetic species in frozen solutions of biomolecules [35] have also been examined. 

An application to clarify the hgand structure of an aqueous Cu complex in ZSM-5 zeolite is shown in Fig. 2.16. The ENDOR spectrum obtained with the 

The FID decays rapidly in solid samples, for which spin echo measurements are better suited. 

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