Magnetic field effects in radical pair recombination. I. CIDNP and CIDEP in geminate recombination

Abstract

The method of analytic solution of the stochastic Liouville equation (SLE) describing geminate radical pair recombination in a magnetic field is developed. The method permits taking into account the exchange interaction J(r) and diffusive relative motion of the radicals. It is based on the sudden perturbation approximation and is valid when ξ=( Q/Dα 2) 1 2 <1, where Q is the characteristic magnetic interaction (hfi, etc.), D is the relative diffusion coefficient and α −1 is the characteristic length factor in the exponential dependence J(r). The solution of the SLE is found as an expansion in ξ up to terms ∼E 2. This solution is applied to derive simple matrix expressions for magnetic field effects (MFEs) such as chemically induced dynamic nuclei (electron) polarization (CIDN(E)P). In the high magnetic field limit in ST 0 approximation the simple analytical formulae for CIDN(E)P are obtained. The formulae derived are quite accurate in a wide range of values of the parameters available in the theory. The high accuracy of these formulae is demonstrated by comparison with the numerical calculations. A number of experimental investigations are analyzed by the formulae of the theory. The analysis shows that in general the SLE formalism makes it possible to describe quantitatively the experiments on MFEs in geminate recombination of radicals.