Electronic and vibrational structures in the S₀ and S₁ states of coronene

We observed the fluorescence excitation spectra and dispersed fluorescence spectra of jet-cooled coronene-h12 and coronene-d12. We analyzed the vibronic structures, assuming a planar and sixfold symmetric molecular structure (D6h). The S1 state was identified to be B2u1. The S1B2u1←S0A1g1 transition is symmetry forbidden, so the 000 band is missing in the fluorescence excitation spectrum. We found a number of vibronic bands that were assigned to the e2g fundamental bands and their combination bands with totally symmetric a1g vibrations. This spectral feature is similar to that of benzene although several strong e2g bands are seen in coronene. The band shape (rotational envelope) was significantly different in each e2g 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 S1 state and the normal coordinate of each e2g vibrational mode, which were obtained by theoretical calculations. The calculated band shapes well reproduced the observed ones, suggesting that the isolated coronene molecule has D6h symmetry.