SHUNJI KASAHARA AND MICHIRU YAMAWAKI, Molecular Photoscience Research Center, Kobe University, Kobe 657-8501, Japan; MASAAKI BABA, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.

Dibenzofuran is one of the prototypical molecule of toxic dioxins and it is great important to investigate the excited-state dynamics. We have observed low-resolution spectra for the vibronic structure of the S1 1A1 leftarrow S0 1A1 transition of jet-cooled dibenzofuran. Several vibronic bands are stronger than the 000 band. These bands are found to be the A-type transition which are enhanced by intensity borrowing through the vibronic coupling with the S2 1B2 state. Rotationally resolved ultrahigh-resolution spectra of jet-cooled dibenzofuran for the 000 and 000+443 cm-1 band have been observed. Several thousand lines were assigned and these molecular constants were determined. We have extended the high-resolution spectroscopic measurement for several vibronic bands up to 1335 cm-1. We analyzed observed rotational lines and determined the molecular constants for each vibronic bands. The Zeeman broadenings of the rotational lines were also observed, and the J, K-dependence were studied. As a result, the observed Zeeman effects could be explained to be originating from the magnetic moment of the S1 1A1 state induced by mixing with S2 1B2 state by J-L coupling.