A quantum-mechanical investigation of O(3P) + CO scattering cross sections at superthermal collision energies

The Martian atmospheric gas loss may have played a role in transforming Mars from a warmer, water-containing planet into a cold and dry one. This loss is attributed to different phenomena, including photodissociation of H₂O followed by Jeans escape and photochemical escape of hot O atoms.  It was proposed that collisions with hot (super-thermal) neutral atoms can eject light species from the atmosphere such as He [1], D[2], H₂ [3], and OH[4]. Here, collisions with super-thermal oxygen atoms are the most important because of its kinetic energy and abundance. Carbon monoxide (CO) has been used as a probe for studying the planet’s atmospheric composition and the dynamics involved [5]. In this study, we computed the elastic and inelastic integral and differential cross-sections for CO collisions with energetic O(³P) and its isotopes using a full coupled-channel quantum mechanical formalism at collision energies from 0.4 to 5 eV. The O+CO interactions were described using recently constructed potential energy surfaces of ³A′, ³A″, and 2³A″ symmetry [6], dissociating to the atomic ground state. The state-to-state, elastic, and inelastic cross-sections were calculated for individual surfaces as well as their statistical average [7]. We applied the new cross sections in a simple 1D column transport model to provide revised escape and energy transfer rates of O(³P) and its isotopes in thermal CO gas, at the conditions corresponding to the upper atmosphere of Mars, where CO is abundant.

References:

[1]       S. Bovino, P. Zhang, F. A. Gianturco, A. Dalgarno, and V. Kharchenko, “Energy transfer in O collisions with He isotopes and Helium escape from Mars,” Geophys. Res. Lett., vol. 38, no. 2, pp. 2–6, 2011, doi: 10.1029/2010GL045763.

[2]       P. Zhang, V. Kharchenko, M. J. Jamieson, and A. Dalgarno, “Energy relaxation in collisions of hydrogen and deuterium with oxygen atoms,” J. Geophys. Res. Sp. Phys., vol. 114, no. 7, pp. 1–14, 2009, doi: 10.1029/2009JA014055.

[3]       M. Gacesa, P. Zhang, and V. Kharchenko, “Non-thermal escape of molecular hydrogen from Mars,” Geophys. Res. Lett., vol. 39, no. 10, pp. 1–6, 2012, doi: 10.1029/2012GL050904.

[4]       M. Gacesa, N. Lewkow, and V. Kharchenko, “Non-thermal production and escape of OH from the upper atmosphere of Mars,” Icarus, vol. 284, pp. 90–96, 2017, doi: 10.1016/j.icarus.2016.10.030.

[5]       M. Zhang and D. Shi, “Transition properties of the X 1 Σ + , I 1 Σ − , A 1 Π , D 1 Δ , B 1 Σ + , and a 3 Π states of carbon monoxide,” Comput. Theor. Chem., vol. 1202, no. May, p. 113302, 2021, doi: 10.1016/j.comptc.2021.113302.

[6]       R. L. Ja, G. M. Chaban, and M. Field, “Collisional Dissociation of CO : ab initio Potential Energy Surfaces and Quasiclassical Trajectory Rate Coe cients,” pp. 1–54, 2019.

[7]       S. Chhabra, M. Gacesa, M. S. Khalil, A. Al Ghaferi, and N. El-kork, “A quantum-mechanical investigation of O(3P) + CO scattering cross sections at superthermal collision energies,” Mon. Not. R. Astron. Soc., no. October, 2022, doi: https://doi.org/10.1093/mnras/stac3057.