Vibrational state dependence of radiationless processes in 1B2u benzene

Abstract

An extensive examination of the vibrational state dependence of fluorescence lifetimes in supersonic jet‐cooled 1 B 2u benzene, and the inferred vibrational state dependence of the nonradiative rate constants, are reported. The qualitative features of our results agree with those obtained from previous investigations using room temperature vapor phase samples. The spectral simplification achieved in the supersonic jet expansion has, however, allowed measurement of the fluorescence lifetimes of a number of 1 B 2u vibrational levels not previously studied. These data indicate that excitation of ν4, ν5, ν8, and ν1 0 result in enhanced nonradiative decay, which suggests that these vibrations are promoting modes. A previously unobserved sensitivity of the nonradiative rate constant to the vibrational angular momentum of the initially excited level has been demonstrated. Finally, fluorescence decays which do not have simple exponential form have been observed from vibrational levels in the vicinity of the ‘‘channel three’’ region. We discuss the significance of all of these observations in terms of the existing theory of radiationless processes and with respect to other recent experimental investigations.