Theory of chemically induced dynamic electron polarization. III. Initial triplet polarizations

An analysis of dynamical aspects of the CIDEP mechanism proposed by Wong et al. is given. This mechanism is based upon the formation of an excited triplet by intersystem crossing that populates the three triplet levels unequally. The subsequent rotational averaging of the initial population distribution coupled with the orientational effects of the zero field splitting is carefully treated in this work utilizing the stochastic Liouville equation in a manner closely analogous to that recently given for ESR line shapes and relaxation of slow−tumbling triplets. It is shown that the predicted CIDEP polarizations can indeed be very substantial, in agreement with Wong et al., but they will depend in general on the relative magnitudes of not only the zero field (D and E) and Zeeman terms (ω0) but also the relevant reaction rates and the rotational tumbling times (τR). A useful perturbation expression valid for D2 ≲ (1/2)[ω02 + τR−2] is obtained which shows these details. Typical complete solutions, obtained numerically, are given for cases when this inequality does not hold.