| Abstract
| - The laser-induced fluorescence (LIF) spectra, both the fluorescence excitation spectra (FES) and singlevibrational level fluorescence spectra (SVLF) from several different vibronic states, along with the ultraviolet(UV) absorption spectra of 1,4-benzodioxan have been recorded and analyzed. A detailed energy map hasbeen constructed for four low-frequency vibrations and their combinations for both the S0 and S1(π,π*)electronic states. These are ν48 (ring-bending), ν25 (ring-twisting), ν47 (ring-flapping), and ν24 (skeletal-twisting).Both the experimental and ab initio calculations show the molecule to be twisted in both the S0 and S1(π,π*)states with high barriers to planarity. The experimentally determined ring-twisting quantum states, which areconfined to the lower regions of the potential energy surface, were used to calculate one-dimensional potentialfunctions in terms of the twisting coordinates, and the extrapolated barriers were estimated to be 5700 and4200 cm-1 for the S0 and S1 states, respectively. Two-dimensional calculations, which included the interactionswith the bending modes, gave values of 3906 and 1744 cm-1, respectively. The S0 value compares favorablywith the ab initio value of 4095 cm-1.
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