The observed transitions were taken from
(1) T. Klaus, S. Takano, and G. Winnewisser, 1997, Astron. Astrophys. 322, L1;
(2) J. Flores-Mijangos, J. M. Brown, F. Matsushima, H. Odashima, K. Takagi, L. R. Zink, and K. M. Evenson, 2004, J. Mol. Spectrosc. 225, 189; and from
(3) F. Lewen, S. Brünken, G. Winnewisser, M. Simecková, and S. Urban, 2004, J. Mol. Spectrosc. 226, 113.
Note: Overlapping features have been treated specially in (2) and (3). In (2), the frequency of the overlapping hyperfine feature was corrected so that the frequency could be attributed to the strongest hyperfine component. In (3), the weights of the hyperfine components were adjusted according to their contribution to the measured frequency of the overlapping lines.
Transitions with uncertainties larger than 100 and 200 kHz for the N = 1 – 0 and all other transitions, respectively, have not been merged.
Also used in the fit were ground state combination differences from an infrared emission spectrum by
(4) R. S. Ram, P. F. Bernath, and K. H. Hinkle, 1999, J. Chem. Phys. 110, 5557. They have been provided by M. S.; see (3).
The dipole moment was taken from
(5) E. A. Scarl and F. W. Dalby, 1974, Can. J. Phys. 52, 1429.