Re-examination of the rotationally resolved spectra of the electronic origin and several vibronic bands of 1,3-benzodioxole

The structure and vibrations of 1,3-benzodioxole are reinterpreted using rotational constants and inertial defects obtained from high resolution electronic spectroscopy. Results are examined in light of previously published theoretical calculations and conclusions are drawn regarding vibrational assignments for transitions to the excited state. Compared to the ground state, the excited S1 state has a significantly more nonplanar geometry (and/or is considerably less rigid), owing to an enhanced anomeric effect involving the oxygen lone pair electrons.