The ground electronic state of magnesium oxide is perturbed by low-lying electronic states. Its rovibrational spectrum can be fit quite well up to v = 2 using effective spectroscopic parameters. The presence of these low-lying electronic states and their perturbation of the ground electronic state affect the partition function. The underestimation may be still quite small at 300 K, but will increase at higher temperatures. An update with treatment of the perturbations may be provided once the molecule will have been detected unambiguously. The purpose of the present fit is to provide data for MgO, ²⁵MgO, and ²⁶MgO in low vibrational states.
An isotopic independent fit was performed by
(1) H. S. P. Müller, 2022, unpublished.
Transition frequencies were taken from
(2) T. Törring and J. Hoeft, 1986, Chem. Phys. Lett. 126, 477.
Additional millimeter and lower submillimeter data (excluding the v = 3 data) were taken from
(3) E. Kagi, and K. Kawaguchi, 2006, J. Mol. Struct. 795, 179.
Also used were rovibrational transitions from
(4) S. Civiš, H. G. Hedderich, and C. E. Blom, 1991, Chem. Phys. Lett. 176, 489.
The parameter set is similar to the one in (2).
The calculated transition frequencies should be viewed with some caution.
²⁵Mg hyperfine splitting was assumed to be negligible for astronomical observations. The dipole moment of the main isotopolog was taken from a quantum-chemical calculation in
(5) H. Thümmel, R. Klotz, and S. D. Peyerimhoff, 1989, Chem. Phys. 129, 417.
Isotopic changes and possibly also rotational changes in the dipole moment can be neglected, vibrational changes possibly not.