Spectroscopic investigations and potential energy surfaces of the ground and excited electronic states of 1,3-benzodioxan.

The laser-induced fluorescence spectra (both fluorescence excitation and dispersed fluorescence) of jet-cooled 1,3-benzodioxan along with its ultraviolet absorption spectra have been recorded and analyzed in order to determine the vibrational quantum levels in both the ground and S(1)(pi,pi()) electronic excited states. A detailed energy map of the vibrational levels involving the six lowest frequency vibrations was established and utilized to better understand the structural and conformational differences between the ground and excited electronic states. The energies of more than a dozen vibrational excited states involving the out-of-plane ring twisting (nu(47)) and the out-of-plane ring bending (nu(48)) modes were determined for both S(0) and S(1) electronic states. Ab initio and density functional theory (DFT) calculations were also carried out to complement the experimental work. The data allowed one-dimensional potential energy functions in terms of the ring-twisting coordinate to be calculated. These show the molecule to have a twisting angle of 33 degrees and a barrier to planarity of 4300+/-500 cm(-1) for the S(0) ground state and an angle of 24 degrees and a barrier of 1500+/-200 cm(-1) for the S(1)(pi,pi()) excited state.