The radiation-induced formation of excited states of aromatic hydrocarbons in benzene and cyclohexane, II. Yields of excited singlet and triplet state solute molecules

The concentration dependences of the yield of excited triplet states, G(3S*), and the concentration dependences of the relative yield of radiation-induced fluorescence obtained on pulse radiolysis of solutions of naphthalene, anthracene, pyrene and 2,5-diphenyloxazole (PPO) are reported. The yields of excited singlet state solute molecules, G(1S*), formed on pulse radiolysis of naphthalene-cyclohexane and naphthalene-benzene solutions has been determined by comparing the intensity of the radiation-induced fluorescence with that obtained on photo-excitation. It is concluded that intersystem crossing (i.s.c.) from the excited singlet state is an important process in the formation of the high yield of triplet excited states of the solute. Under certain conditions this process accounts for up to 50 % of G(3S*) in cyclohexane and the entire G(3S*) in benzene solutions.