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The Ka = 1 transition data were taken
from
(1) A. J. Apponi, M. E. Sanz, C. A. Gottlieb, M. C. McCarthy, and P. Thaddeus,
2001, Astrophys. J. 547, L65.
Even values of Ka do not exist because of the symmetry
of the molecule. Omitting one line with large residual and employing
one additional parameter, the data fit well to the standard 2 kHz,
substantially better than the suggested 5 kHz. Extrapolation to
higher Ka is not possible.
The calculated spectrum should be sufficiently reliable up to 3 mm.
This should be sufficient for observations in cold sources.
The dipole moment is from a quantum-chemical calculation by
(2) T. D. Crawford, J. F. Stanton, J. C. Saeh, and H. F. Schaefer, III,
1999, J. Am. Chem. Soc. 121, 1902.
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