On the antiphase structure of the ESR spectra of spin-correlated radical pairs. Dependence on dimensionality

The ESR lineshape of spin-correlated radical pairs (RP) diffusing in a small volume is calculated within the sudden perturbation approach for space dimensionalities D = 1, 2, 3. It is shown that in 2D and 3D models the RP spin dynamics are described by a Bloch-type equation quite accurately. A simple formula for the antiphase structure of the ESR lines is derived. The results obtained differ essentially from those predicted in the quasistatic approximation.