Gas phase absorption spectra and decay of triplet benzene, benzene-d(6), and toluene

Transients formed when benzene and toluene are excited by energy transfer from Hg(P-3(0)) atoms were investigated by a modulation type kinetic spectroscopy method. Broad transient absorption bands were observed with maxims at 231.5 nm for benzene and 240.0 nm for toluene. Their oscillator strength was estimated to be 0.06. These absorptions were attributed to the hydrocarbon triplet state and assigned to the E-3(2g)+ - B-3(1u)- electronic transition of benzene. Kinetic measurements indicated that the decay of the triplet state is not determined by a unimolecular process. Lifetimes as long as 0.5 msec were observed and could be explained as due to impurity quenching. Lifetime shortening at higher triplet formation rates occurred in a way consistent with an extremely rapid triplet-triplet bimolecular process. Secondary transients were observed in each hydrocarbon, and identified as triplet biphenyl in the case of benzene.