Vibronic Structure in the S1−S0 Transition of Jet-Cooled Dibenzofuran

Fluorescence excitation spectra of dibenzofuran in a supersonic jet are observed and the vibronic structure is analyzed for the S1 1A1 (ππ*) and S0 states. An observation of the rotational envelopes reveals that the band is a B-type band. However, it is shown that most of the strong vibronic bands are A-type bands. The intensity arises from vibronic coupling with the S2 1B2 state. We find a broad emission in the dispersed fluorescence spectrum for the excitation of the high vibrational levels in the S1 state. This indicates that intramolecular vibrational redistribution (IVR) occurs efficiently in the isolated dibenzofuran molecule.