Quantum scattering of hot H/D on CO$_2$: Cross sections and rate coefficients for planetary atmospheres and their evolution
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| Format: | Preprint |
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2025
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| _version_ | 1866914218635165696 |
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| author | Bop, Cheikh T. Gacesa, Marko |
| author_facet | Bop, Cheikh T. Gacesa, Marko |
| contents | Collisions between hot hydrogen atoms and CO$_2$ play a central role in energy transfer and atmospheric escape in CO$_2$-rich planetary atmospheres. We present quantum mechanical $j_z$-conserving coupled-states calculations of state-resolved cross sections for H/D--CO$_2$ collisions at energies up to 5~eV, benchmarked to within 7\% of close-coupling results. Scattering is strongly forward-peaked, yielding momentum-transfer cross sections substantially smaller than commonly assumed: mass-scaling from O/C--CO$_2$ systems overestimates H--CO$_2$ total cross sections by factors of 30--45, while existing empirical fits underestimate the low-energy regime by up to $\sim$45\%. Isotopic substitution (H/D) produces energy-dependent differences of up to 35\% at $E<0.1$~eV, invalidating uniform scaling approaches for D/H fractionation. Maxwellian-averaged rate coefficients derived from our cross sections are significantly smaller than mass-scaled values, implying reduced H--CO$_2$ energy transfer efficiency. In atmospheric escape modelling, these revisions can shift Martian exobase altitudes by 10--20~km, leading to order-unity changes in thermal escape rates, and have implications for hydrogen loss in early CO$_2$-dominated planetary atmospheres. Our results provide essential quantum-mechanical inputs for revisiting atmospheric evolution scenarios on Mars, early Earth, and CO$_2$-rich exoplanets. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2512_21044 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Quantum scattering of hot H/D on CO$_2$: Cross sections and rate coefficients for planetary atmospheres and their evolution Bop, Cheikh T. Gacesa, Marko Earth and Planetary Astrophysics Atmospheric and Oceanic Physics Chemical Physics Space Physics Collisions between hot hydrogen atoms and CO$_2$ play a central role in energy transfer and atmospheric escape in CO$_2$-rich planetary atmospheres. We present quantum mechanical $j_z$-conserving coupled-states calculations of state-resolved cross sections for H/D--CO$_2$ collisions at energies up to 5~eV, benchmarked to within 7\% of close-coupling results. Scattering is strongly forward-peaked, yielding momentum-transfer cross sections substantially smaller than commonly assumed: mass-scaling from O/C--CO$_2$ systems overestimates H--CO$_2$ total cross sections by factors of 30--45, while existing empirical fits underestimate the low-energy regime by up to $\sim$45\%. Isotopic substitution (H/D) produces energy-dependent differences of up to 35\% at $E<0.1$~eV, invalidating uniform scaling approaches for D/H fractionation. Maxwellian-averaged rate coefficients derived from our cross sections are significantly smaller than mass-scaled values, implying reduced H--CO$_2$ energy transfer efficiency. In atmospheric escape modelling, these revisions can shift Martian exobase altitudes by 10--20~km, leading to order-unity changes in thermal escape rates, and have implications for hydrogen loss in early CO$_2$-dominated planetary atmospheres. Our results provide essential quantum-mechanical inputs for revisiting atmospheric evolution scenarios on Mars, early Earth, and CO$_2$-rich exoplanets. |
| title | Quantum scattering of hot H/D on CO$_2$: Cross sections and rate coefficients for planetary atmospheres and their evolution |
| topic | Earth and Planetary Astrophysics Atmospheric and Oceanic Physics Chemical Physics Space Physics |
| url | https://arxiv.org/abs/2512.21044 |