The molecule is the slightly higher lying enol form of methylglyoxal. The latter is also known as acetylformaldehyde and pyruvaldehyde. The molecule was studied in the regions 128 to 166 and 285 to 329 GHz by
(1) J. Koucký, L. Kolesniková, K. Luková, K. Vávra, P. Kania, A. Coutens, J.-C. Loison, J. K. Jørgensen, A. Belloche, and Š. Urban, 2022, Astron. Astrophys. 666, Art. No. A158.
Also included were very accurate microwave data from
(2) F. J. Lovas, R. D. Suenram, D. F. Plusquellic, and H. Møllendal, 2003, J. Mol. Spectrosc. 222, 263.
The uncertainties from (2) were slightly conservative in (2) and even more so in (1); implicitely assumed uncertainties were used for the data from (1). Use of the S reduction required two distortion parameters less in the fit which is usually beneficial for the calculated frequencies. Moreover, the S reduction is more versatile and yields frequently better fits. The calculations should be sufficient for all observational purposes. Transition frequencies with calculated uncertainties larger than 200 kHz should be viewed with caution.
The experimental dipole moment components were determined in (2).