The formation of the solute excited triplet states via geminate ion recombination observed for both biphenyl and pyrene solutions in cyclohexane has been studied by using a picosecond pulse radiolysis system for absorption spectroscopy with the time resolution of 8o ps. The ratio of the formation rate of the solute excited triplet state of the decay rate of the solute anion changes in a time range between 5 and 20 ns. It is very well correlated with the spin correlation decay of geminate ion pairs, which are initially paired with each other in a singlet state. The formation of the solute triplet state was observed even on a timescale shorter than 5 ns, although loss of spin correlation is negligibly small.
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