The experimental lines were reported by
(1) H. S. P. Müller, A. Brahmi M., J.-C. Guillemin, F. Lewen, and S. Schlemmer, 2021, Astron. Astrophys. 647, Art. No. A179.
The data have been truncated at J = 50 and 500 GHz. Transition frequencies involving K_a > 12 should be viewed with caution.
The dipole moment of the main isotopolog was determined by
(2) R. C. Benson, W. H. Flygare, M. Oda, and R. Breslow, 1973, J. Am. Chem. Soc. 95, 2772.
Assuming the isotopic change in the dipole moment to be negligible, the b-component was derived in (1) from the structure and through quantum-chemical calculations.