On the theory of chemically induced electron polarization (CIDEP): Vector model and an asymptotic solution

Abstract

It is shown that the stochastic–Liouville model of CIDEP can be cast into the form of a ’’Bloch-type’’ equation with diffusion. This leads to a generalized vector model of the radical pair mechanism of chemically induced magnetic polarization, which gives a clear picture of the qualitative features of both CIDNP and CIDEP. For the case of simple Brownian motion of the two radicals the differential form of the stochastic–Liouville equations of CIDEP is readily converted into a single integral equation. In the limit of slow singlet–triplet mixing by the magnetic spin Hamiltonian, and with an exchange interaction that decays exponentially with radical separation, this integral equation may be solved exactly. The electron polarization then takes the form of a superposition of an infinite number of ’’contact exchange modes’’.