Electron spin echo envelope modulation spectroscopy with g-value and orientation filters

Two new electron spin echo envelope modulation (ESEEM) experiments, electron-Zeeman (EZ) ESEEM and right-angle wiggling (RAW) ESEEM, are introduced. The experiments are based on the combination of a one- or two-dimensional ESEEM sequence with an EZ-EPR or RAW-EPR detection scheme. The approaches provide considerably enhanced g-value and orientation filters as compared to the standard ESEEM experiments. EZ-ESEEM facilitates the disentangling of overlapping nuclear frequencies along a g-value dimension for systems with anisotropic g-matrices, whereas with RAW-ESEEM overlapping frequency components along a dimension that is related to the change in resonance frequency when the orientation is varied, can be separated. The underlying concepts are outlined and the new experiments are illustrated by numerical simulations and examples of applications.