A three level kinetic model is fitted to fluorescence intensities measured as a function of excitation intensity for theS0toS2transition of isolated diphenylhexatriene. Parameters derived in the fit are coupled with experimental observations to bracket the rate of energy redistribution fromS2to vibrationally excited levels ofS1andS0to between 1010and 4times;1012sminus;1. The rate of excitation, which is directly proportional to oscillator strength, is precisely determined in the fit to be 3.7times;108sminus;1per mgr;J at the peak of our 6 ns FWHM laser pulse.
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