MAGNETIC-FIELD DEPENDENCE OF NUCLEAR-SPIN POLARIZATION AS A CRITERION FOR THE TRIPLET-OVERHAUSER MECHANISM

The magnetic field dependence of nuclear spin polarization effects is evaluated as a mechanistic criterion for the triplet-Overhauser mechanism. The relation between CIDNP intensity and magnetic field strength is generally complex since at least three of the four steps of this mechanism are magnetic field dependent. The effects observed during the photoreaction of trifluoroacetophenone with dimethoxybenzene in acetonitrile show a high field maximum, which is compatible with the triplet-Overhauser mechanism, and two low field maxima, which can be assigned to S-T± mixing in a radical ion pair. These assignments were confirmed by the quencher concentration dependence at the fields that give rise to maximum effects. © 1980 American Institute of Physics.