The S0 → S4 transition jet-cooled fluoranthene: vibronic coupling of S4 with S3

The S1→S0 fluorescence excitation spectrum of fluoranthene in a continuous supersonic jet was measured in the region of the S0→S4 absorption band. The vibrational structure of S4 was studied up to excess energies of ≈1600 cm−1 above the S4, 0 origin at ≈ 35664 cm−1. In total 19 vibronic transitions were observed. The origin of the S0 → S4 absorption band consists of at least two transitions, S0, 0 → S4, 0′ (Γ4, 0′ ≈ 89 cm−1) and S0, 0 → S4, 0′ (Γ4, 0″ ≈ 79 cm−1), whose contributions to the 0, 0 band can be described by Lorentzian line profiles. The lower limit of the lifetime of S4, 0 was estimated to be ⪆ 60 fs. In the overlapping region of the S4, 0 absorption band and the {S3, w} manifold, fluoranthene exhibits intermediate-level structure; the vibronic coupling S4 ⇔ S3 can be classified as a strong intermediate case.