Vibrational magnetism and the strength of magnetic dipole transition within the electric dipole forbidden v2 + v3 absorption band of carbon dioxide

The theory of vibrational magnetism in symmetric linear molecule is reviewed and extended taking an isolated CO2 molecule as example. The order of magnitude of the magnetic-dipole transition moment is evaluated for the nominally forbidden v(2) + v(3) absorption band. Our consideration is inspired by a recent observation of an unconventional series of spectral lines obeying Delta f = 0, +/- 1 selection rules in the Martian atmosphere near 3.3 mu m [A. Trokhimovskiy, V. Perevalov, O. Korablev, A.A. Fedorova, K.S. Olsen, J.-L. Bertaux, A. Patrakeev, A. Shakun, F. Montmessin, F. Lefevre, and A. Lukashevskaya, Astron. Astrophys. 639, A142 (2020)] assigned to magnetic transitions within v(2) + v(3) absorption band in (CO2)-C-12-O-16. Here we adduce arguments that the assignment of these lines requires further examination. It is shown that the integrated intensity of v(2) + v(3) band derived from either observation in the Martian atmosphere or in the laboratory controlled conditions exceeds notably the value which might be theoretically expected for the magnetic-dipole transition. [GRAPHICS] .

Automated summary

The theory of vibrational magnetism in symmetric linear molecules is reviewed and extended using an isolated CO2 molecule as an example. The study explores unconventional spectral lines observed in the Martian atmosphere near 3.3 μm, which are believed to be magnetic transitions within the v(2) + v(3) absorption band in (CO2)-C-12-O-16. Results suggest that further examination is needed for the assignment of these spectral lines, as their characteristics exceed the theoretically expected values for magnetic-dipole transitions.