The pulse radiolysis technique has been used to measure the yields of excited singlet and triplet states in benzene and p-xylene. In pure p-xylene transitory absorption spectra can be observed which are associated with the excimer, the triplet state, and a biradical. Similar data have been obtained in benzene. By energy transfer to suitable polycyclic aromatic compounds it is found that G(singlet) = 1.70 in benzene, G(singlet) = 2.05, and G(triplet) = 2.35 in p-xylene. Unlike the benzene triplet in which the half-life is 3.5 nsec, the p-xylene triplet has a half-life of 28 nsec. The yields and data in benzene and p-xylene are discussed in terms of conventional radiolytic mechanisms in aromatic compounds, in which the triplet states may be formed directly or by ion neutralization.

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