The Pedersenndash;Freed theory of chemicallyhyphen;induced dynamic spin polarization is extended to low field cases where theTplusmn;rarr;Stransitions must be included. The solutions of the stochastichyphen;Liouville equation are again obtained by numerical finitehyphen;difference (FD) methods, but order of magnitude reductions in the size of the matrices to be inverted are realized by introduction of a simple modification of the FD expressions. The simplest case of a single nuclear spin ofI=1/2 on one radical is treated in detail. The results show unequivocally the significant dependence of both CIDNP and CIDEP signals on both the magnitude and the range of the exchange interaction. Also, significant polarizations which should be observable are predicted for both types of experiment under appropriate low field conditions. All the computed results are consistent with a simple qualitative model involving two primary regions inrspace: in the outer region the hyperfine terms induceTplusmn;rarr;Stransitions andJ(r) =0, while in the inner regionJ(r) modulates the effectiveness of these transitions. Consideration is also given to magnetichyphen;field effects on chemical reactivity as well asTplusmn;rarr;Scontributions in high field but viscous CIDEP.
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