Microwave spectrum of glycerol: Observation of a tunneling chiral isomer

The microwave spectrum of the sugar alcohol glycerol (CH2OHCHOHCH2OH) has been measured over the frequency range 8.2-26.5 GHz with a pulsed-beam Fourier-transform microwave spectrometer. Five conformers of glycerol have been assigned and identified with the aid of ab initio electronic structure calculations. One of the higher energy conformers exhibits tunneling of the three hydroxyl groups along a chiral inversion pathway similar to the tunneling of the C2 polyol, ethylene glycol. Stark effect measurements were carried out on several of the lowest energy conformers to provide accurate determinations of the dipole moment components.