Inhomogeneous contribution to the width of zero-field MARY line

The paper discusses the dependence of the singlet product yield in the recombination of radical ion pairs vs. external magnetic field in a situation when hyperfine couplings in one partner are much greater than those in the other partner. The theoretical calculations performed for the case of equivalent magnetic nuclei demonstrate a considerable effect of small hyperfine couplings on the shape of this dependence. In particular, the width of the low-field magnetic field effect (referred to as the 'zero-field' MARY line) is determined by weak hyperfine interactions along with spin coherence lifetime. The predictions are in a qualitative agreement with experimental results.