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The sign of the Overhauser effect for protons in Mn++ aqueous solutions in external fields between 5 and 20 gauss is such, that the dominant relaxation mechanism is scalar coupling between the protons and electron spins. The electronic ΔF = 0, ΔmF = ±1 transitions in the hyperfine multiplet were saturated and the enhancement of the proton resonance signal with increasing electronic saturation was observed up to a factor of about 300 times. The dependence of the proton and electron relaxation times on external field agree well with a theory which takes due account of the hyperfine multiplet in the Mn++ ion.
Codrington et al. (1958) studied this question.