Non‐thermal escape of molecular hydrogen from Mars

Abstract

[1] We present a detailed theoretical analysis of nonthermal escape of molecular hydrogen from Mars induced by collisions with hot atomic oxygen from the Martian corona. To accurately describe the energy transfer in O + H 2 (v, j) collisions, we performed extensive quantum-mechanical calculations of state-to-state elastic, inelastic, and reactive cross sections. The escape flux of H 2 molecules was evaluated using a simplified 1D column model of the Martian atmosphere with realistic densities of atmospheric gases and hot oxygen production rates for low solar activity conditions. An average intensity of the non-thermal escape flux of H 2 of 1.9 Â 10 5 cm À2 s À1 was obtained considering energetic O atoms produced in dissociative recombinations of O 2 + ions. Predicted ro-vibrational distribution of the escaping H 2 was found to contain a significant fraction of higher rotational states. While the non-thermal escape rate was found to be lower than Jeans rate for H 2 molecules, the non-thermal escape rates of HD and D 2 are significantly higher than their respective Jeans rates. The accurate evaluation of the collisional escape flux of H 2 and its isotopes is important for understanding non-thermal escape of molecules from Mars, as well as for the formation of hot H 2 Martian corona. The described molecular ejection mechanism is general and expected to contribute to atmospheric escape of H 2 and other light molecules from planets, satellites, and exoplanetary bodies. Citation: Gacesa, M., P. Zhang, and V. Kharchenko (2012), Non-thermal escape of molecular hydrogen from Mars,

Atmospheric Escape Processes and Planetary Atmospheric Evolution

“…Gacesa et al. (2012) proposed a very similar mechanism where the impact of hot O from the Martian corona sputters light gases. Their computations suggest that it is the main channel for HD and D 2 direct escape.…”

Non-thermal production and escape of OH from the upper atmosphere of Mars

“…are the initial and final RV levels of H 2 and OH, respectively. The cross sections of Gacesa et al (2012) are adopted for elastic scattering. Both sets of cross sections were constructed in an extended collision energy range for purposes of modeling non-thermal atmospheric processes and high-temperature combustion.…”

Quantum reactive scattering of O(3P)+H2 at collision energies up to 4.4 eV

“…We believe that a larger basis set used in the current study is able to better account for higher rotational states populated during the reaction, yielding somewhat larger cross sections. Note that the oscillations present for higher partial waves in the previous high resolution calculation 4 are due to the centrifugal barrier of the rotating atom-molecule composite.…”

“…4,52 For example, QM scattering calculation of suprathermal collisions of atmospheric gases and hot O atoms in planetary atmospheres has been used to estimate the reactions' contribution to formation of extended planetary a) gacesa@phys.uconn.edu b) kharchenko@phys.uconn.edu coronae, 53 and predict a new escape mechanism of molecular hydrogen from the martian atmosphere. 4 In this article, we report the results of state-to-state quantum scattering calculations of O( 3 P)+H 2 reactive collision in the energy interval from 0.4 to 4.4 eV, using recent chemically accurate 3 A and 3 A PESs. 6,29 We compare our results with existing QM calculations and QCT calculations, as well as with the results of molecular beam measurements.…”

“…The O( 3 P)+H 2 reaction represents a prototype chemical process of considerable interest in combustion, 1 as well as in atmospheric [2][3][4] and interstellar 5 chemistry. Owing to its relative simplicity, as well as to the fact that the reaction has an energy barrier of about 0.56 eV below which it proceeds via an abstraction mechanism, 6 it is suitable for benchmarking theoretical methods and experiments.…”