THE S-0-]S-4 TRANSITION OF JET-COOLED FLUORANTHENE - VIBRONIC COUPLING OF S-4 WITH S-3

The S-1 --> S-0 fluorescence excitation spectrum of fluoranthene in a continuous supersonic jet was measured in the region of the S-0 --> S- 4 absorption band. The vibrational structure of S-4 was studied up to excess energies of approximate to 1600 cm(-1) above the S-4,S-0 origin at approximate to 35664 cm(-1). In total 19 vibronic transitions were observed. The origin of the S-0 --> S-4 absorption band consists of a t least two transitions, S-0,S-0 --> S-4,S-0' (Gamma(4,0') approximate to 89 cm(-1)) and S-0,S-0--> S-4,S-0'' (Gamma(4,0'') approximate to 7 9 cm(-1)), whose contributions to the 0, 0 band can be described by Lo rentzian line profiles. The lower limit of the lifetime of S-4,S-0 was estimated to be greater than or similar to 60 fs. In the overlapping region of the S-4,S-0 absorption band and the {S-3,S-w} manifold, fluo ranthene exhibits an intermediate-level structure; the vibronic coupli ng S-4 double left right arrow S-3 can be classified as a strong inter mediate case.