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 60 GHz. In addition, the hyperfine structure splitting should be viewed with some caution below 6 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).