Rotational spectra of two conformers of 1,3-propanediol have been studied very recently. Both display tunneling because of a double-minimum potential, similar to ethanediol. a'GG'g is the lower energy coformer. Spin-statistics were ignored because of the similarity of the weights. Both conformers have been studied recently extensively at millimeter wavelengths by
(1) I. A. Smirnov, E. A. Alekseev, V. I. Piddyachiy, V. V. Ilyushin, and R. A. Motiyenko, 2013, J. Mol. Spectrosc. 293–294, 33.
Also used in the fit were Fourier transform microwave data reported by
(2) D. F. Plusquellic, F. J. Lovas, B. H. Pate, J. L. Neill, M. T. Muckle, and A. J. Remijan, 2009, J. Chem. Phys. A 113, 12911.
The a'GG'g conformer was calculated to be the lowest one with the gGG'g conformer 150 K higher in energy. Other conformers were calculated to be more than 300 K higher. The conformers were treated as separate molecules for the evaluation of the partition function.
The predictions should be sufficiently accurate for all astronomical observations. They should be viewed with caution if the uncertainties are larger than 0.5 MHz.
The dipole moment was calculated in (2).