The data set of the second entry of Dec. 2011 was revised considerably. Transition frequencies up to J = 12 – 11 were provided in v = 0 more as an orientation. However, transitions up to J = 9 – 8 were identified in space with JWST recently. While frequencies up to J" = 6 were good enough because of the available experimental data, extrapolations for the highest two transitions were, unsurprisingly, not satisfactory.
The present data set is restricted to v = 0. Starting parameters were derived from the first 15 theoretically calculated electric dipole rotational transitions based on
(1) H. Jóźwiak, H. Cybulski, and P. Wcisło, 2020, J. Quant. Spectrosc. Radiat. Transfer, 253, Art. No 107171.
These data were subjected to an Euler-type Hamiltonian. As in the second entry, the J" = 0 transition frequency was taken from
(2) B. J. Drouin, S. Yu, J. C. Pearson, and H. Gupta, 2011, J. Mol. Struct., 1006, 2.
The J = 2 – 0 ground state combination difference was published by
(3) F. M. J. Cozijn, M. L. Diouf, and W. Ubachs, 2022, Eur. Phys. J. D, 76, Art. No. 220;
while the J = 3 – 1 ground state combination difference was given in
(4) F. M. J. Cozijn, M. L. Diouf, V. Hermann, E. J. Salumbides, M. Schlösser, and W. Ubachs, 2022, Phys. Rev. A, 105, Art. No. 062823.
These highly accurate data have uncertainries between 25 and 30 kHz. In addition, the J = 4 – 3 frequency was taken from
(5) L. Ulivi, P. de Natale, and M. Inguscio, 1991, Astrophys. J., 378, L29,
and the J = 4 – 3 and 7 – 6 frequencies were taken from
(6) P. Essenwanger and H. P. Gush, 1984, Can. J. Phys., 62, 1680.
Other transition frequencies from (5) and (6) were omitted because of their large residuals with respect to the reported uncertainties. Please note that the J = 4 – 3 transition frequency from (6) may well be omitted also because of its large uncertainty compared to the one from (5). Since the calculated transition frequencies based on (1) were very well compatible with the first three frequencies, it was sufficient to release the lowest order parameter (corresponding to B) to obtain a satisfactory fit. As the resulting uncertainties of the calculated transition frequencies were deemed too small, the next higher order parameter was released also, yielding an uncertainty of 2.77 MHz for the J = 12 – 11 frequency and in agreement within this uncertainty with the initial value (1). The frequencies should be sufficiently accurate for astronomical observations, but might be viewed with some caution for the highest J in the case of laboratory measurements with very high accuracies.
The new dipole moment and its first rotational correction were derived from results of quantum chemical calculations by
(7) K. Pachuki and J. Komasa, 2008, Phys. Rev. A, 78, Art. No. 052503.
The rotationless value is in very good agreement with experimental determinations employing intensity measurements as well as other theoretical values. The older value of 0.000585 D is definitively incompatible with these numbers. The experimental determinations are hampered by large pressure shifts as well as by high pressure effects on the intensities.
The partition function takes into account both vibrational states. Some caution is advised for the highest temperature value.