The first entry from Feb. 2018 was sufficient for observations in cold sources. The new entry will satisfy observers should they want to search for the molecule in hot environments. New and very extensive millimeter and submillimeter data were reported by
(1) L. Margulès, B. A. McGuire, C. J. Evans, R. A. Motiyenko, A. Remijan, J.-C. Guillemin, A. Wong, and D. McNaughton, 2020, Astron. Astrophys. 642, Art. No. A206.
Additional low frequency data were taken from
(2) R. D. Brown, P. D. Godfrey, R. Champion, and M. Woodruff, 1982, Aust. J. Chem. 35, 1747;
and from
(3) K. N. Crabtree, M.-A. Martin-Drumel, G. G. Brown, S. A. Gaster, T. M. Hall, and M. C. McCarthy, 2016, J. Chem. Phys. 144, Art. No. 124201.
Two additional parameters were added compared to (1). The a-type transitions in (1) display on average smaller residuals than the b-type transitions, but no adjustments were made. The original line list of (2) was used with the reported uncertainties. A fair fraction of the data in (3) appear to be judged very conservatively and some optimistically; on average, the uncertainties are appropriate. The original uncertainties were thus used, in contrast to the first version.
The calculations are sufficiently accurate for all observational purposes. Transition frequencies with calculated uncertainties larger than 0.2 MHz should be viewed with caution.
The experimental dipole moment is from (2).