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 should be viewed with caution above 70 GHz.
The partition function takes into account the higher spin component as far as possible at present.
The dipole moment of the main species is from a quantum chemical calculation in (1).