Electronic and vibrational structures in the S 0 and S 1 states of coronene

We observed the fluorescence excitation spectra and dispersed fluorescence spectra of jet-cooled coronene- h 12 and coronene- d 12 . We analyzed the vibronic structures, assuming a planar and sixfold symmetric molecular structure ( D 6 h ). The S 1 state was identified to be B 2 u 1 . The S 1 B 2 u 1 ← S 0 A 1 g 1 transition is symmetry forbidden, so the 0 0 0 band is missing in the fluorescence excitation spectrum. We found a number of vibronic bands that were assigned to the e 2 g fundamental bands and their combination bands with totally symmetric a 1 g vibrations. This spectral feature is similar to that of benzene although several strong e 2 g bands are seen in coronene. The band shape (rotational envelope) was significantly different in each e 2 g mode. It was shown that degenerate rotational levels were shifted and split by the Coriolis interaction. We calculated the Coriolis parameter using the molecular structure in the S 1 state and the normal coordinate of each e 2 g vibrational mode, which were obtained by theoretical calculations. The calculated band shapes well reproduced the observed ones, suggesting that the isolated coronene molecule has D 6 h symmetry.