The majority of the rotational lines are from
(1) M. Caris, F. Lewen, and G. Winnewisser, 2002, Z. Naturforsch. 57a, 663. Additional lower frequency data are from
(2) P. L. Clouser and W. Gordy, 1964, Phys. Rev. 134, 863.
Further, new lower frequency data are from
(3) C. Cabezas, J. Cernicharo, G. Quintana-Lacaci, I. Peña, M. Agundez, L. Velilla Prieto, A. Castro-Carrizo, J. Zuñiga, A. Bastida, J. L. Alonso, and A. Requena, 2016, Astrophys. J. 825, Art. No. 150;
and from
(4) B. A. Timp, J. L. Doran, S. Iyer, J.-U. Grabow, and K. R. Leopold, 2012, J. Mol. Spectrosc. 271, 20.
Rovibrational transitions were taken from
(5) R. S. Ram, M. Dulick, B. Guo, K.-Q. Zhang, P. F. Bernath, 1997, J. Mol. Spectrosc. 183, 360;
from
(6) H. Uehara, K. Horiai, K. Nakagawa, and T. Fujimoto, 1989, J. Mol. Spectrosc. 134, 98;
and from
(7) K. Horiai, T. Fujimoto, K. Nakagawa, and H. Uehara, 1989, Chem. Phys. Lett. 147, 133.
The analysis follows largely that in (3), meaning that data for the ³⁵Cl and ³⁷Cl isotopologs were fit together.
²³Na and ³⁶Cl hyperfine splitting is negligible except possibly for very low values of J.
Predictions should be reliable throughout for v up to at least 4. The partition function takes into account all states up to v = 30. The dipole moments were calculated according to an empirical formula from
(8) F. H. de Leeuw, R. van Wachem, and A. Dymanus, 1970, J. Chem. Phys. 53, 981;
with the vibrational contributions corrected according to the Born-Oppenheimer approximation.