Tunnelling splittings in the rotational spectrum of 3-fluoro-benzylalcohol

The rotational spectra of 3-fluoro-benzyl alcohol and of its OD isotopologue have been measured by free jet absorption millimeter wave spectroscopy. The spectrum is consistent with a gauche conformation of the oxygen atom, characterized by a OCα–C1C2 dihedral angle of approximately 50°, and with the hydroxyl group zusammen with respect to the F atom. μc-Type transitions are split into two evenly spaced component lines by ≈1.64 MHz, showing that the CH2OH group undergoes a tunnelling motion which connects two equivalent minima above and below the aromatic ring. The barrier to inversion has been calculated to be 155 cm−1.