Rotational band contour analysis of symmetries and interactions of vibrational levels in anthracene S1

Over 50 of the more intense transitions in the S1 excitation spectrum (0–2000 cm−1 of vibrational energy) of supersonic jet-cooled anthracene are investigated using rotational band contour analysis, including computer simulations. This allows unambiguous assignment of the vibrational symmetries of all levels below 1100 cm−1 and many levels at higher energies, some of which were unassigned previously. Using complementary narrow-band excitation and energy-resolved detection techniques, a Fermi resonance at 755 cm−1 is thoroughly investigated to obtain the energy separation of the unperturbed states and the magnitude of the coupling matrix element. Levels which showed restricted or dissipative intramolecular vibrational-energy redistribution in time-resolved experiments (1380, 1420, and 1792 cm−1) are also studied.