The experimental data was taken from
(1) D. Christen, L. H. Coudert, R. D. Suenram, and F. J. Lovas, 1995 J. Mol. Spectrosc. 172, 57 and from
(2) D. Christen and H. S. P. Müller, 2003 Phys. Chem. Chem. Phys. 5, 3600.
Lines with uncertainties of larger than 100 kHz have not been merged. The frequency cut-off has been set to 600 GHz in order to limit the size of the catalog entry.
The aGg' conformer of ethylene glycol, also know as ethandiol, is the lowest state conformer. The OH groups undergo a concerted large amplitude tunneling motion during rotation. Hence, every rotational level is split into two labeled by state quantum numbers 0 and 1. State 1 is 6957.8 MHz higher.
Transitions with a and c selections rules are between the two tunneling states while b-type transitions are withing the states.
Predictions should be quite reliable if J ≤ 40 and K_a ≤ 15. Spin-statistics have been taken into account.
The dipole moment was published in (1).