Abiotic molecular oxygen production—Ionic pathway from sulfur dioxide

Abstract

Molecular oxygen, O 2 , is vital to life on Earth and possibly also on exoplanets. 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 O 2 from SO 2 , a chemical constituent of many planetary atmospheres and one that played an important part on Earth in the Great Oxidation Event. The O 2 production involves dissociative double ionization of SO 2 leading to efficient formation of the O 2 + ion, which can be converted to abiotic O 2 by electron neutralization or by charge exchange. This formation process may contribute substantially to the abundance of O 2 and related ions in planetary atmospheres, such as the Jovian moons Io, Europa, and Ganymede. We suggest that this sort of ionic pathway for the formation of abiotic O 2 involving multiply charged molecular ion decomposition may also exist for other atmospheric and planetary molecules.

Fragmentation dynamics of CH3Clq+ (q = 2,3): theory and experiment

“…Instead, we observe in majority the H + + CH 2 Cl 2+ and the H 2 + + CHCl 2+ products. This may suggest some state selectivity upon fragmenting CH 3 Cl 3+ ions as recently evidenced by some of us for SO 2 2+ unimolecular decomposition forming the less favorable thermodynamically SO 2+ + O 46 and O 2 + + S + 47 ion pairs in addition to the obvious SO + + O + ion pair. 46 Such experiments on polyatomic triply charged ions are still challenging in particular upon valence triple ionization because of the low abundance of triple ionization compared to single and double ionization processes.…”

“…For other molecular systems, such experiments combined with advanced theoretical treatments allowed elucidating the unimolecular state-to-state reaction pathways undertaken by the doubly changed molecular ions formed by valence double photoionization of the corresponding neutral. 46,47,49,50…”

Energetic electron irradiations of amorphous and crystalline sulphur-bearing astrochemical ices

“…and de SouzaBonfim et al (2017) have demonstrated that electronically excited SO2 may also abstract oxygen atoms from either an adjacent SO2 molecule or from a O2 molecule; the latter having likely been formed as a result of the double ionisation of the SO2 parent molecule followed by electron neutralisation as described recently byWallner et al (2022): parent molecule decay trends and in the abundance of molecular products observed after irradiation were noted between the studied amorphous and crystalline ice phases.…”

“…SO 3 formation in irradiated SO 2 ices has been studied extensively and is believed to be the result of the dissociation of the latter species to yield free oxygen atoms which may then bond with other SO 2 molecules ( Moore et al, 2007b ). It should be noted, however, that earlier studies by Pilling and Bergantini (2015) and de Souza Bonfim et al (2017) have demonstrated that electronically excited SO 2 may also abstract oxygen atoms from either an adjacent SO 2 molecule or from a O 2 molecule; the latter having likely been formed as a result of the double ionisation of the SO 2 parent molecule followed by electron neutralisation as described recently by Wallner et al (2022) : …”

SO2 Photodissociation at 193 nm Directly Forms S(3P) + O2(3Σg–): Implications for the Archean Atmosphere on Earth

“…Although the SO 2 mixing ratio in the Archean atmosphere is not believed to have exceeded 2 ppbv, R1b is a direct source of O 2 that would contribute to the increase of O 2 partial pressure. Other proposed sources of photogenerated O 2 in Earth’s early atmosphere include the photodissociation CO 2 → h ν C( 3 P) + O 2 at photon energies of 11.7–12.2 eV and a recent report of double ionization of SO 2 using 40.81 eV photons yielding normalO 2 + + S + . The CO 2 photodissociation pathway producing O 2 is similar to channel R1b in many respects, although it requires a significantly higher-energy photon.…”