The data set includes rotational data from
(1) M. Godon and A. Bauer, 1974, C. R. Acad. Sci. Paris, Ser. B 278, 113.
The J = 4 – 3 and 7 – 6 transitions displayed residuals mostly much larger than the suggested 60 kHz uncertainties and were omitted. In contrast, the remaining transitions had residuals within 30 kHz. Several higher order parameters were estimated from the main isotopic species. The calculations have been truncated at J = 25 because of the somewhat limited data set and should, in addition, be viewed with caution at higher J and K.
The dipole moment of the main isotopic species was taken from
(2) M. Römheld, 1978, PhD thesis, Univerität Ulm, Germany.