Pulse Radiolysis Studies of Acetone Solutions of Biphenyl and Anthracene: Formation of Ions and Excited Singlet State

Abstract

The radiolysis of acetone solutions of biphenyl and anthracene has been studied by means of the microsecond-pulse technique. Transient spectra, as well as the effects of ion scavengers, show the presence of both positive and negative ions of biphenyl and anthracene in irradiated solutions. Assuming that molar extinction coefficients of positive and negative ions are identical, one can determine the yields of ions to be G(biphenyl++biphenyl−) = 1.1 at 0.69M, and G(anthracene++anthracene−) = 1.5 at concentrations above 5 × 10−3M. Decay kinetics of aromatic ions fit the second-order rate law, which can be ascribed to the charge neutralization reaction between the positive and negative ions; rate constants are found to be k(biphenyl++biphenyl−) = 3.9 × 1011 M−1·sec−1 and k(anthracene++anthracene−) = 2.6 × 1011 M−1·sec−1. The light emitted upon irradiation of acetone solutions of anthracene is anthracene fluorescence; a part of fluorescence is delayed. The relationship between the intensity of fluorescence and the concentration, as well as the comparison of the energy level of anthracene with that of acetone, suggests the occurrence of energy transfer from the first excited singlet state of acetone to anthracene. The rate constant of energy transfer is estimated to be 6 × 1010M−1·sec−1. The yield of excited singlet anthracene is determined to be G(1anthracene) = 0.31 at the concentration of 1.0 × 10−2M. Addition of various ion scavengers to acetone solutions of anthracene reduces the yields of both excited singlet and triplet anthracene. These results may be explained by the reactions of ion scavengers with the primary ions in spurs. Thus these reactions result in the decreases in the yields of excited acetone which may be produced by geminate recombination.