Spectroscopic Studies and Ab Initio Calculations of 1,3-Benzodioxan in its S$_{0}$ and S$_{1}(\pi $,$\pi $*) Electronic States*

Both the ground (S$_{0})$ and excited [S$_{1}(\pi $,$\pi $*)] states of 1,3-benzodioxan have been studied using molecular spectroscopy and theoretical calculations. Infrared, Raman, ultraviolet absorption, and laser-induced fluorescence (LIF) spectroscopies of the jet-cooled molecules were used to create energy maps for the vibrational and vibronic levels of the molecule, especially for the low-frequency vibrational modes which help to elucidate the conformational energetics of the molecule. The ring-bending, twisting, and flapping motions of the molecule provide the pathways for the conformational changes and were studied in considerable detail. The molecule is twisted with a high barrier to planarity of the equilibrium structure.