The mechanism of excited state formation in radiolysis of hydrocarbon liquids

The fluorescence intensity of bicyclohexyl liquid excited both with β particles and with 184.9 nm light has been studied as a function of the concentration of perfluorocarbon electron scavengers. From this it has been possible to estimate (a) the fraction of all excited singlet states which derive from geminate ion pairs and (b) the probability (averaged over the spur size distribution) that a geminate ion pair will generate an excited singlet state on recombination. The latter value is compared with theoretical values and it is concluded that in bicyclohexyl the geminate electron does not spin-relax prior to recombination. Preliminary results for p-xylene are also presented and important differences between the saturated and aromatic hydrocarbon liquids are discussed.