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.
Please note that this calculation does not include ¹H hyperfine structure splitting as it is very unlikely resolvable in the ISM. The calculations should be accurate enough for observational purposes; increasing caution is advised for N > 10.
The transition 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.
Please note that the intensities may be described insufficiently by the transition dipole moment alone. Therefore, intensities should be viewed with some caution.