The entry is based on a fit of all available field free data of the OH⁺ main isotopolog published by
(1) W. G. D. P. Silva, L. Schneider, U. U. Graf, H. S. P. Müller, P. Jusko, A. M. Jacob, D. Riechers, S. Schlemmer, and O. Asvany, 2026, Phys. Chem. Chem. Phys., accepted.
The work includes highly accurate hyperfine-resolved low-N infrared transition frequencies along with N = 1 – 0 and 2 – 1 rotational transition frequencies obtained with microwave accuracy.
Further v = 1 – 0 infrared data with megahertz accuracies were taken from
(2) C. R. Markus, J. M. Hodges, A. J. Perry, G. S. Kocheril, H. S. P. Müller, and B. J. McCall, 2016, Astrophys. J. 817, Art. No. 138.
Particularly noteworthy are also vibration-rotation transitions up to v = 5 – 4. These were published in
(3) B. D. Rehfuss, M.-F. Jagod, L.-W. Xu, and T. Oka, 1992, J. Mol. Spectrosc. 151, 59.
Also retained in the fit were the N = 1 – 0 rotational transition frequencies with HFS splitting were taken from
(4) J. P. Bekooy, P. Verhoeve, W. L. Meerts, and A. Dymanus, 1985, J. Chem. Phys. 82, 3868;
as well as the N = 13 – 12 transition frequencies with FS splitting were reported in
(5) D.-L. Liu, W.-C. Ho, and T. Oka, 1987, J. Chem. Phys. 87, 2442.
The calculations should be accurate enough for observational purposes; increasing caution is advised for N > 5. The ¹H hyperfine structure splitting should be viewed with slight caution because vibrational changes to the HFS parameters could not be determined yet.
The electric dipole moment is from a quantum chemical calculation by
(6) H.-J. Werner, P. Rosmus, and E.-A. Reinsch, 1983, J. Chem. Phys. 79, 905.