Abiotic Molecular Oxygen Production - Ionic Pathway From Sulphur Dioxide

Panel A shows electron pairs measured in coincidence with two ions in red (from fourfold events) and one ion in purple (from threefold events) upon photoionisation of SO2 at 40.81 eV photon energy. For comparison, the black curve is a higher resolution electron pair only spectrum of the total double ionisation at the same photon energy previously discussed in Ref. [26]. The bar combs mark the vertical ionisation energies computed at the MRCI/aug-cc-pV(Q+d)Z level of theory at the neutral SO2 [X 1A1] ground state equilibrium geometry, i.e. at an O–S–O angle of 120◦ and R = 2.7 Bohr. Panel B shows a breakdown diagram of the major detectable decay channels of doubly ionised SO2. Panel C indicates schematically the stable isomers of SO2+ 2 , which are accessible in the energy region where O+ 2 + S+ is detectable.

Molecular oxygen, O2, is vital to life on Earth and possibly on other planets. Although the biogenic processes leading to its accumulation in Earth's atmosphere are well understood, its abiotic origin is still not fully established.

Here, we report combined experimental and theoretical evidence for electronic-state-selective production of O2 from SO2, a major chemical constituent of many planetary atmospheres and one which played an important part on Earth in the Great Oxidation event. The O2 production involves dissociative double ionisation of SO2 leading to efficient formation of the O+2 ion which can be converted to abiotic O2 by electron neutralisation. We suggest that this formation process may contribute significantly to the abundance of O2 and related ions in planetary atmospheres, especially in those where CO2, which can lead to O2 production by different mechanisms, is not the dominant component.

Måns Wallner, Mahmoud Jarraya, Saida Ben Yaghlane, Emelie Olsson, Veronica Ideböhn, Richard J. Squibb, Gunnar Nyman, John H.D. Eland, Raimund Feifel, Majdi Hochlaf

Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Chemical Physics (physics.chem-ph)
Cite as: arXiv:2108.12672 [astro-ph.EP] (or arXiv:2108.12672v1 [astro-ph.EP] for this version)
Submission history
From: Raimund Feifel
[v1] Sat, 28 Aug 2021 16:17:35 UTC (1,258 KB)
Astrobiology, Astrochemistry

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