The manifestation of degenerate electron exchange in stimulated nuclear polarization at high magnetic fields Original Research Article

A detailed theoretical and experimental investigation of the degenerate electron exchange (DEE) effect on the stimulated nuclear polarization (SNP) intensity and spectra at high magnetic fields has been made. The theoretical description of DEE processes is performed in two different ways: (i) The numerical solution of equations of noncorrelated frequency migration theory and (ii) the analytical solution for simple two-site model for the dependence of the SNP intensity on the rate of DEE at low microwave (mw) field amplitudes (B1 ⪡ a, a is a constant of hyperfine interaction (HFI) of radical-ions) and low DEE rates (aτe ⪢ 1, τe is the characteristic time of DEE). It is shown that the increase of DEE rate leads to the decrease of splitting in SNP spectra, and also to a substantial decrease of the SNP signal intensity due to an overlapping of hyper-fine structure lines with opposite signs. A numerical evaluation of DEE rate constants can be done by comparison of experimental and calculated spectrum shape in the case of fast DEE rates and from the dependence of SNP intensity in resonance on the concentration of diamagnetic molecules.