Methyl deuterated acetaldehyde consists of two different conformers, the in-plane conformer and the doubly degenerate out-of-plane conformer, which is about 15.55 cm^–1 or 22.38 K higher in energy than the latter. The barrier to tunneling between the two equivalent out-of-plane conformations is sufficiently low to facilitate tunneling, thus lifting the degeneracy upon rotation. Rotation-tunneling interaction is strong between the two out-of-plane conformations, in part also between these and the in-plane conformer, especially for the symmetric (+) tunneling component.
The catalog entry and the fit are described in
(1) L. H. Coudert, L. Margulès, C. Vastel, R. Motiyenko, E. Caux, and J.-C. Guillemin, 2019, Astron. Astrophys. 624, Art. No. A70;
most of the experimental frequencies were taken from that work. Additional frequencies below 40 GHz were taken from
(2) P. H. Turner and A. P. Cox, 1976, Chem. Phys. Lett. 42, 84;
and from
(3) P. H. Turner, A. P. Cox, and J. A. Hardy, 1981, J. Chem. Soc. Faraday Trans. 2 77, 1217;
for the in-plane and out-of-plane conformers, respectively. Predictions with uncertainties larger than 0.2 MHz should be viewed with caution. Predictions of transitions involving strongly interacting levels may have to be viewed cautiously even if uncertainties are very small.
The vibrational identifier 0 refers to the in-plane conformer and 1 and 2 to the symmetric (+) and antisymmetric (–) tunneling states, respectively, of the out-of-plane conformer.
The partition function includes approximate contributions from the lowest torsional mode and from the lowest small amplitude vibration. The partition function should thus be fairly well converged up to about 100 K.
The dipole moment values were calculated in (1).