Electronic and vibrational structures in the S and S states of coronene.

We observed the fluorescence excitation spectra and dispersed fluorescence spectra of jet-cooled coronene-h and coronene-d. We analyzed the vibronic structures, assuming a planar and sixfold symmetric molecular structure (D). The S state was identified to be B2u1. The SB2u1←SA1g1 transition is symmetry forbidden, so the 0 band is missing in the fluorescence excitation spectrum. We found a number of vibronic bands that were assigned to the e fundamental bands and their combination bands with totally symmetric a vibrations. This spectral feature is similar to that of benzene although several strong e bands are seen in coronene. The band shape (rotational envelope) was significantly different in each e 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 state and the normal coordinate of each e 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 symmetry.