The Dunham fit follows largely
(1) R. H. Petrmichl, K. A. Peterson, and R. C. Woods, 1988, J. Chem. Phys. 89, 5454.
Rovibrational data were also included. These were taken from
(2) Y. Akayama, K. Tanaka, and T. Tanaka, 1989, Chem. Phys. Lett. 155, 15.
The dipole moments were taken from a quantum-chemical calculation by
(3) K. A. Peterson, R. C. Woods, P. Rosmus, and H.-J. Werner, 1990, J. Chem. Phys. 93, 1889.
Transition frequencies should be reliable up to 900 GHz, possibly higher.
The partition function takes excited vibrational states into account.