Peculiarities of magnetic field and spin effects in a three-spin system with regard to the long-distance character of exchange interaction

The biradical recombination probability and its field dependence in the presence of a paramagnetic particle was calculated in balance approximation taking into account the extended character of the exchange interaction in the biradical. Previously, to describe the effect of the third spin on the spin evolution in the biradical, we considered the constant spin exchange interaction both inside the biradical and between the added spin and one of the paramagnetic biradical centers. In the present work we considered the long-distance character of the exchange interaction of the biradical with the third spin. It is shown that the field dependence retains the main characteristic peculiarities of the three-spin system in the approximation of the constancy of the exchange interaction, i.e., the existence of several extrema, their shift along the field depending on the values of the exchange integrals, and the existence of a field-independent, nonzero recombination probability, known as spin catalysis.