Version 1 of Nov. 2005 was revised considerably. A combined fit of v = 0, v₁₁ = 1 μ²Σ, and v₁₁ = 1 ²Δ was performed. The initial millimeter data were reported by
(1) H. Linnartz, T. Motylewski, O. Vaizert, J. P. Maier, A. J. Apponi, M. C. McCarthy, C. A. Gottlieb, and P. Thaddeus, 1999, J. Mol. Spectrosc. 197, 1.
Initial hyperfine split ²Π_3/2 FTMW data were published by
(2) M. C. McCarthy, W. Chen, A. J. Apponi, C. A. Gottlieb, and P. Thaddeus, 1999, Astrophys. J. 520, 158.
Further hyperfine split FTMW data were published by
(3) C. A. Gottlieb, M. C. McCarthy, and P. Thaddeus, 2010, Astrophys. J. Suppl. Ser. 189, 261.
Perturbations between v = 0 and v₁₁ = 1 μ²Σ appear to be negligible. The parameter b_F was identical within uncertainties for the three vibrational states, and the values were thus locked to the same value. Additional distortion parameters were applied in comparison to (1). The calculation was truncated at 300 GHz, transition frequencies should be reliable up to that frequency.
At low frequencies, the ¹H hyperfine splitting was resolved both in the laboratory and in space. Therefore, a separate calculation with hyperfine splitting is available up to 50 GHz. NOTE: the partition function does take into account the hyperfine splitting as well as the two excited vibrational states!
The dipole moment is from an ab initio calculation by
(4) D. E. Woon, 1995, Chem. Phys. Lett. 244, 45.
Please note that the dipole moment may be slightly overestimated because of some mixing between the ²Π_i and the ²Σ state.