Fluorescence decay of pyrene vapour; biphotonic excitation and the kinetics of vibrational redistribution

A computer simulation procedure has been applied to the fluorescence decay curves of pyrene vapour, excited into the S₁ state with short laser pulses. The results confirm that the kinetic model which has been used previously in order to describe the effect of vibrational redistribution on the fluorescence decay, is consistent with the experimental decay curves. A very short decay component (τ ≈ 4 nsec) which appears when the energy of the laser exceeds 1.5 mJ is ascribed to doubly excited pyrene molecules.