The measurements of the lower spin component were taken from
(1) M. C. McCarthy, A. L. Cooksy, S. Mohamed, V. D. Gordon, and P. Thaddeus, 2003, Astrophys. J. Suppl. Ser. 144, 287.
The calculation may be sufficiently accurate throughout. Uncertainties are too high above 72 GHz. In addition, the hyperfine structure splitting should be viewed with some caution below 8.8 GHz.
The partition function takes into account the higher spin component as far as possible at present. It is converged at 150 K. The slight incompleteness at higher T has negligible effect on the calculated intensities.
The dipole moment of the main species is from a quantum chemical calculation in (1).