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Abstract:
The laser-induced fluorescence excitation of 3-hydroxyflavone, cooled by seeding in a supersonic expansion of He, has been investigated in the wavenumber range 28000–28500 cm−1. The vibronic origin of the S0-S1 (ππ*) electronic transition of the unperturbed normal molecular form was found at 28080.3 cm−1 (3560.21 Å). The excitation spectrum is characterised by several progressions with vibrational spacing of 45 cm−1, and by severe spectral congestion at excess vibrational energy above 225 cm−1. The prominent vibronic bands are best represented by Lorentzian lineshapes. They are homogeneously broadened with widths (deconvoluted fwhm) varying from 4.1 to 2.6 cm−1. The corresponding vibronic lifetimes, in the range 1.3–2.0 ps, are short because of excited-state intramolecular proton transfer.
