High resolution molecular beam spectroscopy of low frequency vibronic bands of the S1<--So electronic transition of 1,3-benzodioxole.

A detailed analysis of some vibronic bands of the S-1 <-- S-0 electronic transition of 1,3-benzodioxole was carried out at high resolution. The rotational structures of these vibronic bands were completely assigned using a rigid rotor Hamiltonian model. From the rotational constants obtained by the assignment of the spectra it has been demonstrated that previous assignment of the spectrum was not completely satisfactory. The reassignment of the vibronic spectrum is necessary also for the correct first estimate of the entity of the anomeric effect in the S-1 electronic excited state. It is evidenced that the experimental data obtainable with the high resolution electronic spectroscopy are mandatory when assigning vibronic spectra of floppy molecules.