Chemically Induced Dynamic Spin Polarization

The Pedersen-Freed theory for chemically induced dynamic spin polarization CIDN(E)P is generalized to include the effects of anisotropic reactivities and anisotropic exchange interactions on the radical-pair mechanism. Detailed results are given for the simple case in which only one radical exhibits anisotropy that is approximated by a cosine distribution, and the rotational and translational motions are described by Brownian diffusion models. The primary effect upon CIDNP is the reduction in A, the reaction probability for the full collision. This effect can be rather accurately approximated by the use of an “effective” spherically symmetric specific rate constant, which depends, to some extent, on the rotational diffusion coefficient due to the effect of rotational relaxation. Thus CIDNP effects are rather well approximated by a spherically symmetric theory with a renormalized A. In the absence of reactivity, CIDEP effects for our model are reasonably well approximated by a spherically symmetric theory with a renormalized exchange interaction, especially for the asymptotic polarizations for large exchange interactions. When, however, there are orientation-dependent reactivities present with substantially greater orientation dependence than the exchange interaction, then significant deviations from a spherically symmetric theory are predicted even for asymptotic polarizations. The relationship to recent experiments is briefly discussed in this light. Anisotropic initial conditions are typically found to be relaxed by the effective rotational diffusion before they can substantially affect the CIDN(E)P observables.