Anisotropy-resolved electron paramagnetic resonance spectroscopy

A two-dimensional held-swept pulsed EPR method, anisotropy-resolved (AR)-EP R, is introduced. AR-EPR is a powerful tool to disentangle the EPR spectra of disordered systems into a second dimension. The technique is based on a stimulated three-pulse echo sequence combined with sample spinning of varia ble frequency around an axis perpendicular to the static magnetic field. In paramagnetic systems with anisotropic interactions, AR-EPR can be applied to improve the spectral resolution, to separate overlapped spectra, to dete rmine small unresolved hyperfine splittings, and to evaluate principal valu es and principal axes directions in cases where this information cannot be obtained from standard held-swept EPR approaches. A detailed theoretical de scription of AR-EPR is given and a number of model calculations are present ed. The potential of the method is demonstrated by several experimental exa mples.