One laboratory and and three astronomical lines were reported by
(1) P. B. Changala, H. Gupta, J. Cernicharo, J. R. Pardo, M. Agúndez, C. Cabezas, B. Tercero, M. Guélin, and M. C. McCarthy, 2022, Astrophys. J. Lett. 940, Art. No. L42.
Except for (B + C)/2, parameters were kept fixed to scaled or unscaled parameters from
(2) A. G. Watrous and R. C. Fortenberry, 2023, Mon. Not. R. Astron. Soc. 518, 5140.
Despite the very limited data, transition frequencies with K_a = 0 should be quite reliable; all others should be viewed with increasing caution.
The dipole moment of the main isotopic species was taken from a quantum-chemical calculation in
(3) S. Itono, K. Takano, T. Hirano, and U. Nagashima, 2000, Astrophys. J. 538, L163;
the value in 3 agree with this value.