Nuclear energy double resonance method

Electron spin resonance (ESR) measures the absorption spectra associated with the energy states produced from the ground state by interaction with the magnetic field. This review deals with the theory of these states, their description by a spin Hamiltonian and the transitions between these states induced by electromagnetic radiation. The dynamics of these transitions (spin-lattice relaxation times, etc.) are not considered. Also omitted are discussions of other methods of measuring spin Hamiltonian parameters such as nuclear magnetic resonance (NMR) and electron nuclear double resonance (ENDOR), although results obtained by these methods are included in Sec. VI. 

For a given value of B, the energies of Am/ = 1 transitions between the nuclear sublevels of a given electronic spin state are much lower than those between the electronic spin components. Information on the amplitude of the wave function of the electron whose spin is responsible for the ESR spectrum at different lattice sites in the vicinity of the centre was obtained by Feher [17] by monitoring the ESR spectrum as a function of the frequencies in the nuclear frequency range, and this technique was called electron nuclear double resonance (ENDOR). Improvements in the sensitivity of ESR can be obtained using optical or electrical detection methods [47]. 

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