The present entry is based on a combined fit of rotational data in the ground and first three excited vibrational states along with FIR data pertaining to the three lowest vibrational bands. The data set concerning the v₁₁ + v₁₈ = 1 rotational transition frequencies is identical to that of the first entry of Aug. 2017.
The v₁₁ = 1 and v₁₈ = 1 states are the lowest two vibrational states which perturb each other via Coriolis interaction. The rotational transition frequencies were reported by
(1) C. Degli Esposti, L. Dore, M. Melosso, K. Kobayashi, C. Fujita, and H. Ozeki, 2017, Astrophys. J. Suppl. Ser., 230, Art. No. 26.
The rovibrational transition frequencies were reported by
(2) M. Melosso, A. Belloche, M.-A. Martin-Drumel, O. Pirali, F. Tamassia, L. Bizzocchi, R. T. Garrod, H. S. P. Müller, K. M. Menten, L. Dore and, C. Puzzarini, 2020, Astron. Astrophys., 641, Art. No. A160.
Extensive ground state rotational data were published by
(3) Y. Motoki, Y. Tsunoda, H. Ozeki, and K. Kobayashi, 2013, Astrophys. J. Suppl. Ser., 209, Art. No. 23.
Additional transition frequencies were taken from
(4) J. N. MacDonald and J. K. Tyler, 1972, J. Chem. Soc. Chem. Comm., 995;
(5) H. M. Pickett 1973, J. Mol. Spectrosc., 46, 335;
(6) M. Bogey, H. Dubus, and J.-C. Guillemin, 1990, J. Mol. Spectrosc., 143, 180;
and from
(7) R. D. Brown, P. D. Godfrey, A. L. Ottrey and J. W. V. Storey, 1977, J. Mol. Spectrosc., 68, 359.
The spectroscopic parameters employed here differ from those in (2) and even more from those in (1).
The calculations should be good enough for all astronomical observations, those with uncertainties exceeding 0.2 MHz should be viewed with caution.
State number 1 corresponds to v₁₁ = 1 and state number 2 to v₁₈ = 1.
Please note that the partition function currently considers only the ground vibrational state. Vibrational factors for a posteriori correction will be provided.
The dipole moment components were assumed to be the same as in the ground vibrational state, see e056507.cat.