Very accurate microwave data along with millimeter data were reported by
(1) S. Thorwirth, P. Theulé, C. A. Gottlieb, M. C. McCarthy, and P. Thaddeus, 2021, Astrophys. J. 662, 1309.
Additional extensive millimeter data were reported by
(2) S. Gruet, A. L. Steber, and M. Schnell, 2020, J. Mol. Spectrosc. 371, Art. No. 111296.
The calculations are sufficiently accurate for observations in cold and lukewarm sources, possibly even beyond. Transition frequencies with uncertainties exceeding 0.1 MHz should be viewed with some caution.
The dipole moment is from a quantum chemical calculation in (1).