Analysis of 14N ESEEM patterns of randomly oriented solids

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Abstract
Simulations of 14N ESEEM patterns for an S=1/2, I=1 spin system with an isotropic hyperfine coupling, in a nonordered solid are reported. The dependence of the simulated patterns on the quadrupole and hyperfine coupling constants, and on the external field strength is examined and discussed. Three distinct types of powder patterns are identified, all of which exhibit discrete peaks. The dependence of the frequency, width, and amplitude of these peaks on the coupling constants and field strength is elucidated in simple terms. The results provide a basis for the interpretation of ESEEM patterns and for the development of experimental tactics: the variation of field strength (electron spin‐excitation frequency) can be used to manipulate modulation depths, select specific nuclei, and ascertain accurate quadrupole coupling constants. The anisotropy of the amplitude of modulation components, its effect on ESEEM powder patterns, and its implications as regards orientation selection experiments are also considered.