ENDOR in single crystals

Several of the advantages with ENDOR measurements in liquid solution also apply for solid samples. Single crystal measurements are particularly informative. 

Commonly employed measurement procedures are summarized below. Detailed accounts have appeared in general textbooks [19-21], and in specialized treatises of radiation effects and of free radicals in solids [22,23]. 

The improved resolution in ENDOR spectra makes it possible not only to measure the hyperfine couplings with high accuracy, but also to observe splittings that are not resolved by ESR. An example is shown in Fig. 2.5 for the malonic acid radical, HCc (COOH)2 [24]. The ESR spectrum is a main doublet due to hyperfine coupling with the H at the Ca position. The resolution is limited by the line-width and the occurrence of forbidden and so-called spin flip lines discussed in Chapter 4. The ENDOR lines denoted V(t and Va are narrower than the ESR lines by more than an order of magnitude. As in the liquid state the intensities between the pair differ due to hyperfine enhancement and relaxation factors. The additional lines in the ENDOR spectrum were examined using the ENDOR Induced ESR (EIE) method described 

Principal values (MHz) Isotropic value (MHz) Dipolar coupling (MHz) Direction cosines with respect to  

Numbers in parentheses are uncertainties in the last significant digit(s) of the corresponding number [24]. 

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Quadmpole interactions for I > Vi nuclei that usually cannot be obtained from ESR are measured by ENDOR in single crystals. 

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