Magnetic field effects in the recombination fluorescence of a three-spin radical ion/biradical ion system

Magnetosensitive radiofluorescence resulting from geminate recombination of a spin triad involving a radical ion and a biradical ion formed radiolytically in non-polar solutions has been investigated theoretically. The effect of exchange interaction in the biradical ion on the kinetics and yield of radiofluorescence has been studied. Hyperfine coupling in the radical ion and in the biradical ion has been taken into account. The existence of local fluorescence resonances at zero magnetic field and at a field close to the value of the exchange integral in the biradical has been predicted theoretically. The latter result provides a basis to determine the exchange integral in short-lived radiolytically generated biradical ions with high accuracy from experiment.