15min:
ULTRAHIGH-RESOLUTION SPECTROSCOPY OF ANTHRACENE.

MASAAKI BABA, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan; KAZUTO YOSHIDA, YOSUKE SEMBA, SHUNJI KASAHARA, Molecular Photoscience Research Center, Kobe University, Kobe 657-8501, Japan.

Rotationally resolved fluorescence excitation spectra of the S1 1B2u leftarrow S0 transition of anthracene-h10 and anthracene-d10 and the change with the magnetic field have been observed in a collimated molecular beam. Recently, the rotational constants in the S0 and S1 states of anthracene-h10 have been reported by Bendkowsky et al. We have assigned about 1000 rotational lines and determined more accurate values. We have also performed theoretical calculations and obtained the molecular structure, of which the rotational constants are almost the same as the experimental values. The Zeeman broadening was very small and approximately the same for anthracene-h10 and anthracene-d10. It indicates that mixing with the triplet state is very small in the S1 1B2u state. The fluorescence quantum yields of anthracene-h10 and anthracene-d10 are 0.67 and 0.13, respectively. It is concluded that the main nonradiative process in the S1 state of the isolated anthracene molecule is not the intesystem crossing to the triplet state, but the internal conversion to the ground state.