Double Electron-Electron Resonance
Determination of distances larger than about 2 nm by EPR with high precision requires pulse EPR experiments that can separate electron-electron couplings from all other contributions to the Hamiltonian and from relaxational broadening. The double electron-electron resonance (DEER) experiment as one of these methods is described and guidelines for its use are given. It is concluded that the experiment requires only minor modifications of commercial hardware and can be used for measurements in the distance range between 1.5 and 8 nm. For distances up to 5 nm, precision in non-crystalline systems is usually limited by conformational distributions rather than by the method. Four-pulse DEER is demonstrated to allow for the determination of broad distance distributions even at the lower end of this distance range by overcoming dead time problems. The measurement of ion cluster sizes and intercluster distances in ionomers is described to exemplify application of this method to a problem for which other methods for distance determination fail.
KeywordsPump Pulse Diblock Copolymer Spin Probe Distance Determination Intercluster Distance
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