Knowledge Bank

Sub-Doppler high-resolution fluorescence excitation spectra of the $S1\leftarrow S0$ transition of dibenzo-p-dioxin (DD) have been observed in a collimated molecular beam. 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 $0.01cm-1$, which were much larger than the instrumental resolution $(0.001cm-1)$. The lifetime of the $S1$ state was evaluated to be about 500 ps.