IMPLICATIONS OF HYPERFINE ANISOTROPY ON THE DETERMINATION OF N-14 QUADRUPOLE INTERACTIONS FROM DOUBLE-QUANTUM ESEEM FREQUENCIES

In a previous investigation of m-DNB (m-dinitrobenzene) adsorbed on activated γ-alumina, we determined 14N quadrupole and hyperfine coupling constants from the frequencies of double-"quantum" peaks in the ESEEM (electron spin-echo envelope modulation) spectra. The anisotropic hyperfine interactions neglected in such analyses can, however, corrupt the values of quadrupole coupling constants. We outline the effects of anisotropic hyperfine interactions on 14N ESEEM double-quantum peaks. We present new ESEEM results obtained at electron spin excitation frequencies of ∼4 GHz. The "tainted" quadrupolar peaks that emerge in these spectra provide an independent measure of the quadrupole coupling constants. The values obtained are in excellent agreement with those found previously. We infer that the magnitude of the anisotropic portion of the hyperfine interaction is much smaller than that of the quadrupole interaction. © 1990 American Chemical Society.