Details on the fit are given in
(1) A. Baudry, K. T. Wong, S. Etoka, A. M. S. Richards, H. S. P. Müller, F. Herpin, T. Danilovich, M. Gray, S. Wallström, D. Gobrecht, T. Khouri, L. Decin, C. A. Gottlieb, K. M. Menten, W. Homan, T. J. Millar, M. Montarges, B. Pimpanuwat, J. M. C. Plane, and P. Kervella, 2023, Astron. Astrophys. 674, Art. No. A125.
The parameter set and the line list are largely based on the extensive isotopic invariant fit by
(2) B. J. Drouin, 2013, J. Phys. Chem. A 117, 10076,
which, in turn, was the basis for the entries in the JPL catalog. The files were retrieved from the JPL catalog archive. We thank B. J. Drouin for the availability of the files. Two poorly determined parameters were omitted, and high-J Λ-doubling transitions were added from astronomical observations in (1) and in
(3) T. Khouri, L. Velilla-Prieto, E. De Beck, W. H. T. Vlemmings, H. Olofsson, B. Lankhaar, J. H. Black, and A. Baudry, 2019, Astron. Astrophys. 623, Art. No. L1.
These data show systematic deviations with respect to the calculation in the JPL catalog.
Please note: The quantum numbers in the CDMS entry are Hund's case (b) quanta as always. They are N, Λ with parity, v, J + 0.5, and F. N + 0.5 = J refers to Π_3/2 throughout, and N – 0.5 = J to the higher lying Π_1/2. Thus, Hund's case (b) quanta are reasonable throughout.
The very extensive data set is described with references in (2). We provide here references for the Λ-doubling transitions and the various types of rotational and spin-flip transitions in v = 1. Λ-doubling transitions with microwave accuracy were reported by
(4) W. L. Meerts, J. P. Bekooy, and A. Dymanus, 1979, Mol. Phys. 37, 425, by
(5) T. Thissen, H. Spiecker, and P. Andresen, 2000, J. Mol. Spectrosc. 200, 277, by
(6) J. A. Coxon, K. V. L. N. Sastry, J. A. Austin, and D. H. Levy, 1979, Can. J. Phys. 57, 649, and by
(7) J. L. Destombes, B. Lemoine, and C. Marlière-Demuynck, 1979, Chem. Phys. Lett. 60, 493.
These publications involve in part multiple measurements up to N = 7 in Π_3/2 and Π_1/2. Astronomical observarions in (3) extend to J = 17.5 for Π_3/2 at accuracies of around 1 MHz.
Rotational transition frequencies with microwave accuracy were reported by (2) and by
(9) T. D. Varberg and K. M. Evenson, 1993, J. Mol. Spectrosc. 157, 55.
Rotational data with good FIR accuracies up to N = 10 were taken from
(10) M. A. Martin-Drumel, S. Eliet, O. Pirali, M. Guinet, F. Hindle, G. Mouret, and A. Cuisset, 2012, Chem. Phys. Lett. 550, 8.
There are additional rovibrational lines in the data set which include some information on the Λ-doubling at higher rotational levels, but it is not clear if this information is sufficient. Therefore, Λ-doubling transitions above 400 and 70 GHz should be viewed with some caution for Π_3/2 and Π_1/2, respectively. Some caution is advised for rotational transitions and transitions involving spin-flip if the calculated uncertainties exceed 1 MHz.
The partition function was evaluated by summing over all states up to F = 50 and v = 9. While the partition function is essentially converged at 3000 K, model deficiencies may make it advisable to view values at 2000 K and higher with some caution.
The v = 1 dipole moment was determined in
(11) K. I. Peterson, G. T. Fraser, and W. Klemperer, 1984, Can. J. Phys. 62, 1502.