EFFECT OF DEUTERATION ON FLUORESCENT LIFETIME OF LIQUID BENZENE

Decay times of neat benzene C6H6 and C 6D6 fluorescence excited by 250-nm light are, respectively, 27 and 32 nsec at 25°C. Measurements made over the range of temperature 5°-35°C both of the pure benzenes and of solutions in cyclohexanes C6H12 and C6D12 show that the solvent is without effect on the measured rates, that at a particular temperature benzene monomer and excimer have the same rate of de-excitation (corresponding to lifetimes of 28 nsec for C6H6 at 25°C and 33 nsec for C6D6 at 22°C), and that the activation energy for internal conversion of monomer in both cases (on certain stipulated assumptions) is 0.28 eV within limits of experimental error. The reduction, by deuterium substitution, in the rate of de-excitation from the monomer is less than the reduction in the rate from excimer and the rate for benzene excimer is indicated to be independent of temperature in the range studied.