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Abstract
A new electron-electron double resonance (ELDOR) relaxation, due to an intramolecular nuclear-spin exchange, was found in the ion-pair systems of quinone anion and alkali cation. The ELDOR reductions in dimethoxy-ethane solutions of 2,5-di-t-butyl-p-benzoquinone (DBQ) anion and potassium ion, DBQ anion and sodium ion, and p-benzoquinone anion and potassium ion are reported as a function of temperature, concentration, and the difference Δv between the two microwave frequencies. When Δv is the frequency difference between two transitions which are exchanged, the ELDOR reductions are independent of concentration and decreases with decreasing temperature.
A quantitative treatment on this type of ELDOR reduction was developed using the density matrix, and the expressions for the ELDOR reductions were derived. The simulated spectra for ELDOR were thus obtained on the basis of these results, and could reproduce well the observed spectra for various experimental conditions. The rate of cation migration was ten times greater than the spin-lattice relaxation rate (W e) for DBQ--K+ at 213 K, and the ELDOR reduction after extrapolation to infinite pump power, became 83 per cent in this case.