15min:

MASAAKI BABA, Graduate School of Science, Kyoto University, Kyoto 606-8501, Japan; ATSUSHI DOI, YOSHIO TATAMITANI, SHUNJI KASAHARA AND HAJIME KATO, Molecular Photoscience Research Center, Kobe University, Kobe 657-8501, Japan.

Sub-Doppler high-resolution fluorescence excitation spectra of the S₁ S₀ transition of dibenzo-p-dioxin (DD) have been observed in a collimated molecular beam.\footnoteM. Baba, A. Doi, Y. Tatamitani, S. Kasahara, and H. Katô, J. Phys. Chem. A , 108, 1388 (2004) The rotational constants in both the S₀ and S₁ states were determined by analysis of the observed rotational contours. The DD molecule has shown to be planar in the S₀ state and folded slightly out-of-plane (butterfly form) in the S₁ state. The observed line widths were about 0.01 cm^-1, which were much larger than the instrumental resolution (0.001 cm^-1). The lifetime of the S₁ state was evaluated to be about 500 ps.