The trans conformer of HONO is the lower energy form; the cis conformer is 95.8 cm^–1 or 137.8 K higher in energy as reported by
(1) W. Tchana Betnga, F. Kwabia Tchana, A. Perrin, L. Manceron, J. Vander Auwera, F. Hindle, and A. Coutens, 2023, J. Quant. Spectrosc. Radiat. Transfer 310, Art. No. 108727.
Microwave transition frequencies were taken from
(2) D. J. Finnigan, A. P. Cox, A. H. Brittain, and J. G. Smith, 1972, J. Chem. Soc., Faraday Trans. II 68, 548.
Millimeter wave data are from
(3) W. C. Bowman, F. C. De Lucia, and P. Helminger, 1981, J. Mol. Spectrosc. 88, 431.
Far-IR frequencies were reported by
(4) A. Dehayem-Kamadjeu, O. Pirali, J. Orphal, I. Kleiner, and P.-M. Flaud, 2005, J. Mol. Spectrosc. 234, 182.
The parameters are almost the same as from the S reduction fit in (4). ¹⁴N hyperfine splitting can probably be neglected for astronomical or atmospheric observations. The transition frequencies should be sufficiently reliable for all observational purposes.
The partition function values refer to the ground vibrational states of both conformers. Vibrational correction factors are provided for a posteriori adjustment.
The dipole moment components were taken from
(5) A. Allegrini, J. W. C. Johns, A. R. W. McKellar, and P. Pinson, 1980, J. Mol. Spectrosc. 79, 446.
NOTE: Fairly pronounced dipole distortion effects were determined in (1) for the b-component of the cis conformer. They should then also be non-negligible for the a-component and for the trans conformer. The modeling of these distortion effects for the cis conformer were unsuccessful; good results for fairly low quantum numbers were insufficient for higher quantum numbers. It is therefore advised to view the intensities of both conformers with some caution.