Electron-Electron Double Resonance

Abstract

Electron Electron Double Resonance (ELDOR) consisting of a strongly saturating continuous wave (CW) pump microwave source and a nonsaturating observing source, can be used in a field swept display to monitor saturation-transfer mechanisms such as Heisenberg Exchange, nitrogen nuclear relaxation, and rotational diffusion. 2D pulse ELDOR techniques known as DEER or PELDOR using two separate microwave frequencies or a similar “2 + 1” technique using a single frequency have been configured for probing dipolar interactions up to 8 nm. Spin-echo ELDOR techniques have been developed to study slow motions in a wide range of biological problems. Two-dimensional Fourier transform techniques permit all combinations of pump and probe frequencies with nanosecond time resolution making it possible to study the microscopic orientations of a system. Multiquantum ELDOR techniques have been developed to measure the transfer of magnetization and not a reduction factor as measured in a field swept ELDOR.