The anti-gauche conformer, also known as the trans-gauche conformer, is the second lowest state conformer of diethyl ether. According to ab initio calculations mentioned in (1), it is 5.40 kJ/mol (452 cm^–1 or 650 K) higher in energy than the anti-anti conformer.
The experimental lines are from
(1) I. Medvedev, M. Winnewisser, F. C. DeLucia, E. Herbst, E. Bialkowska-Jaworska, L. Pszczólkowski, and Z. Kisiel, 2004, J. Mol. Spectrosc. 228, 314;
and submillimeter data from
(2) A. Walters, H. S. P. Müller, F. Lewen, and S. Schlemmer, 2009, J. Mol. Spectrosc. 257, 24.
The predictions with uncertainties larger than 0.5 MHz should be viewed with caution.
The dipole moment is from an ab initio calculations mentioned in (1).
As in (1), spin-statistics have not been taken into account because the nuclear spin-weight ratio is very close to 1. Tunneling is negligible in this conformer.
Note: The partition function was calculated assuming the energy difference to the lowest conformer to be zero. No vibrational states have been considered in the calculation of the partition function and thed intensities; the energy of this conformer was also not considered. Note also that the symmetry weight of the ag to aa conformers is 2 : 1.