Vibronic coupling and intramolecular dynamics of pyrene as revealed by the S0→S2 excitation spectrum in a supersonic jet

The fluorescence excitation spectrum of pyrene obtained in a supersonic jet for the S₀→S₂ transition shows a complicated structure due to the interaction of discrete levels of S₂ with the quasi-continuous levels belonging to S₁. The intensity distribution pattern in this region has been evaluated from quantum-mechanically calculated quantities, such as the vibronic coupling integrals, and Franck-Condon factors deduced from independent experiments. The dynamics in pyrene following excitation into S₂ are discussed.