The CIDNP kinetics in recombination of successive radical pairs

A theory of chemically induced dynamic nuclear polarization (CIDNP) formed in recombination of successive radical pairs (PRs) is developed. The theory is based on that of RP recombination with the spin Hamiltonian instantaneously changing in time. With kinematics approximation it is shown that general relations for CIDNP are fully expressed via the quadratures of Green functions, which characterize the molecular motion of reagents. Analytical formulae for the time dependence of CIDNP both of primary and secondary RPs have been derived in the strong magnetic field approximation (S-T₀ approximation); field dependences of stationary CIDNP effect for some model cases have been analyzed. For long-lived systems the sensitivity of secondary RP CIDNP to the singlet-triplet evolution of primary RP has been demonstrated. It is shown that sometimes the correct analysis of the effect calls for taking into account the reactivity anisotropy.