Electron-Zeeman resolved electron paramagnetic resonance spectroscopy

Electron-Zeeman (EZ) resolved electron paramagnetic resonance (EPR) spectro scopy is introduced. In this two-dimensional pulse EPR technique a sinusoid al external field DeltaB(0)(t) of variable amplitude is applied during the pulse sequence, resulting in a field-swept EPR spectrum that is spread into a second dimension, representing the g values of the paramagnetic species. The method can be used to improve the resolution of polycrystalline and si ngle-crystal EPR spectra. For polycrystalline systems, simplified EPR spect ra are obtained for fixed g values. For axial symmetry, these spectra allow direct access to coupling constants, also at orientations that differ from the principal axes orientations. Furthermore, overlapping resonances can b e disentangled, extra-absorption peaks identified and unresolved hyperfine splittings observed. The sum projection onto the g-value axis corresponds i n a g-value spectrum, which is free of hyperfine interactions. A detailed t heoretical description of the EZ-EPR experiment is given. Several model cal culations for systems with different symmetry of the magnetic interaction t ensors are presented, and the versatility of EZ-EPR is demonstrated for dif ferent paramagnetic systems with g anisotropy. (C) 2001 Academic Press.