  We have explored the manifold physical scenario emerging from a model of
Dynamic Nuclear Polarization (DNP) via thermal mixing under the hypothesis of
highly effective electron-electron interaction. When the electron and nuclear
reservoirs are also assumed to be in strong thermal contact and the microwave
irradiation saturates the target electron transition, the enhancement of the
nuclear polarization is expected to be considerably high even if the
irradiation frequency is set far away from the centre of the ESR line (as
already observed by Borghini) and the typical polarization time is reduced on
moving towards the boundaries of said line. More reasonable behaviours are
obtained by reducing the level of microwave saturation or the contact between
electrons and nuclei in presence of nuclear leakage. In both cases the function
describing the dependency of the steady state nuclear polarization on the
frequency of irradiation becomes sharper at the edges and the build up rate
decreases on moving off-resonance. If qualitatively similar in terms of the
effects produced on nuclear polarization, the degree of microwave saturation
and of electron-nucleus contact has a totally different impact on electron
polarization, which is of course strongly correlated to the effectiveness of
saturation and almost insensitive, at the steady state, to the magnitude of the
interactions between the two spin reservoirs. The likelihood of the different
scenario is discussed in the light of the experimental data currently available
in literature, to point out which aspects are suitably accounted and which are
not by the declinations of thermal mixing DNP considered here.
