Structure, dipole moment and large amplitude motions of 1-benzofuran.

The rotational spectrum of 1-benzofuran has been investigated by three different rotational spectroscopy techniques: (i) millimeterwave absorption free jet spectroscopy, useful for a fast assignment of the spectrum; (ii) molecular beam Fourier transform microwave spectroscopy, sensitive to detect less abundant isotopic species in natural abundance; (iii) waveguide conventional microwave spectroscopy, useful for the study of intramolecular dynamics, through the rotational spectra of the vibrational satellites of low energy modes. Besides the rotational spectrum of the ground state of the normal species, the spectra of 9 singly substituted 13C and 18O isotopomers in natural abundance, and of 6 vibrational satellites, have been measured. Precise structural parameters for the molecule, as well as information on the potential energy surface of the low energy vibrations, have been obtained. The dipole moment components have been determined to be micro(a)= 0.216 (2) and micro(b)= 0.720 (3) D, respectively.