The Dunham fit was described in
(1) O. Asvany, C. R. Markus, K. Nagamori, H. Kohguchi, J. Furuta, K. Kobayashi, S. Schlemmer, and S. Thorwirth, 2021, Astrophys. J. 910, Art. No. 15.
The rotational data are from that work, the rovibrational data were taken from
(2) M. Gruebele, M. Polak, G. A. Blake, and R. J. Saykally, 1986, J. Chem. Phys. 85, 6276.
The ground state dipole moment was taken from a quantum-chemical calculation by
(3) K. A. Peterson, R. C. Woods, P. Rosmus, and H.-J. Werner, 1990, J. Chem. Phys. 93, 1889.
Transition frequencies should be reliable up to about 500 GHz.
The partition function takes excited vibrational states into account.