The experimental data was taken from
(1) D. Christen, L. H. Coudert, J. A. Larson, and D. Cremer, 2001 J. Mol. Spectrosc. 205, 185 and from
(2) H. S. P. Müller and D. Christen, 2004 J. Mol. Spectrosc., in press.
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 gGg' conformer of ethylene glycol, also know as ethandiol, is the second lowest state conformer. According to (2), it is about 200 cm^–1 higher in energy than the aGg' conformer, see e062503.cat.
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 1367.4 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 <= 6 or if K_a ≤ J ≤ 12. Spin-statistics have been taken into account. NOTE: The partition function was calculated as if gGg' ethylene glycol were an isolated species, i.e. with the 0₀₀ level of state 0 set to zero ! Therefore, one has to consider the energy difference of about 200 cm^–1 for proper intensity calculations if thermal equilibration has been achieved !
The dipole moment components have been estimated in (2) from relative intensity measurements assuming the total dipole moment to be essentially the same as for the aGg' conformer.