Quantum beats in recombination of spin-correlated radical ion pairs with equivalent protons

Quantum beats caused by the hyperfine coupling (hfc) with magnetically equi valent protons were observed in the recombination fluorescence of the singl et-correlated pairs of secondary radical ions generated in cyclohexane solu tions by ionizing radiation. In agreement with theoretical predictions, the ratio I-H(t)/I-0(t) of fluorescence decay kinetics in high and zero magnet ic fields showed narrow peaks for the radical cations with an even number o f the equivalent protons. To generate radical pairs, p-terphenyl-d(14) was used as an electron acceptor while the solvent holes were trapped by octame thyl-1,4-cyclohexadiene, tetramethylethylene, 9,10-octalin, cis-decalin, he xamethylbenzene, durene, p-diethylbenzene, p-xylene, or benzene. When diiso propylamine was used as a hole acceptor, a trough was observed instead of t he strongest peak. The position of the strongest peak (trough) is determine d by the value of hfc constant only and is independent of the number of pro tons. (C) 2000 Published by Elsevier Science B.V. All rights reserved.