Ion-molecule reaction plays crucial roles in interstellar space and atmosphere and drives the matter evolutions therein. Solar winds contain lots of helium ions (He⁺), thus the He⁺ reactions with atmospheric molecules deserve attentions. Meanwhile, a staggering 95% of the Martian atmosphere is carbon dioxide (CO₂), and the Venusian boasts a remarkable 97%. Therefore, the He⁺ collisional reactions with CO₂ contribute to the developments of intricate celestial milieus. Another fundamental issue is the origin of atmospheric O₂. The components of the ancient Earth’s atmosphere (4 billion years ago) are believed as the same as the current Martian, namely, very few O₂ molecules, besides the large quantity of CO₂, do exist in the atmospheres. The prebiotic production of those O₂ molecules attracts considerable interests.

 A cascade process,

CO₂ + hν → CO + O  (1a)

O + O + M → O₂ + M   (1b)

has been recommend as the primordial source of the prebiotic origin of atmospheric O₂ in textbooks^1,2. Another photochemistry channel was proposed recently, 

CO₂ + hν (extreme ultraviolet) → C + O₂  (2)

by Lu et al³. Moreover, the direct production of O₂ was also found in dissociative electron attachment to CO₂,

CO₂ + e¯ → C¯ + O₂       (3)

by Wang et al⁴. More recently, we demonstrate that the ion-molecule reaction,

He⁺ + CO₂ → C⁺ + He + O₂   (4)

is also an important channel⁵. All of these channels are summarized in Figure 1, providing a multichannel picture about the prebiotic origins of O₂ in the CO₂-rich atmospheres. It is noted that the identifications of the O₂ production from above channels (equations 2-4) benefit much from ion velocity map imaging technique.

Figure 1. Prebiotic origins of atmospheric O₂.

References

1. Schopf, J. W. Precambrian Paleobiology: Problems and Perspectives. Annu. Rev. Earth Planet. Sci. 3, 213-249 (1975).
2. Kasting, J. F., Liu, S. & Donahue, T. Oxygen levels in the prebiological atmosphere. J. Geophys. Res. 84, 3097-3107 (1979).
3. Lu, Z., Chang, Y.-C., Yin, Q.-Z., Ng, C. Y. & Jackson, W. M. Evidence for direct molecular oxygen production in CO₂ photodissociation. Science 346, 61-64 (2014).
4. Wang, X.-D., Gao, X.-F., Xuan, C.-J. & Tian, S. X. Dissociative electron attachment to CO₂ produces molecular oxygen. Nat. Chem. 8, 258-263 (2016).
5. Zhi, Y.; Guo, Q.; Xie, J.; Hu, J. & Tian, S. X. Direct production of molecular oxygen from carbon dioxide and helium ion collisions. Commum. Chem. 6, 267 (2023).