Herein, it is argued that Mars has nearly ideal conditions for CO 2 decomposition by nonequilibrium plasmas. It is shown that the pressure and temperature ranges in the 96% CO 2 Martian atmosphere favour the vibrational excitation and subsequent up-pumping of the asymmetric stretching mode, which is believed to be a key factor for an efficient plasma dissociation, at the expense of the excitation of the other modes. Therefore, gas discharges operating at atmospheric pressure on Mars are extremely strong candidates to produce O 2 efficiently from the locally available resources.
This work proposes a complete and consistent set of cross sections for electron impact collisions with carbon monoxide (CO), to be published in the IST-Lisbon database with LXCat. The set is validated by comparing swarm parameters calculated using the two-term Boltzmann solver LoKI-B with available experimental data. A severe inconsistency between the total rotational and effective cross sections reported in the literature for low values of the electron energy (ò<0.1 eV) is pointed out. It is shown that inelastic and superelastic collisions involving rotationally excited levels, as well as superelastic collisions with the first vibrational excited level, have to be taken into account to accurately calculate the electron energy distribution function. The relevance of these mechanisms implies a dependence of the effective momentum transfer cross section on the gas and vibrational temperatures and suggests its replacement by an elastic momentum transfer cross section. The electron kinetics in CO 2 -CO mixtures are also discussed in detail, namely the influence of vibrational excitation and of the CO 2 /CO ratio on the electron energy distribution function, rate coefficients and power transfer. The vibrational temperatures of both CO and the different vibrational modes of CO 2 have a marked influence on the results, due to the importance of superelastic collisions with the vibrationally excited states of both gases. The presence of CO in the mixture modifies the energy transfer pathways and, at moderate reduced electric fields (∼30−100 Td), the vibrational excitation of CO can become the dominant energy loss mechanism, affecting the input of electron energy into the asymmetric stretching mode of CO 2 .
It has been recently advocated that Mars has excellent conditions for oxygen and fuel production directly from atmospheric CO 2 using non-equilibrium plasmas. The Martian conditions would be favorable for vibrational excitation and/or enhanced dissociation by electron impact, two important pathways for CO 2 plasma dissociation. Herein we confirm these theoretical predictions by measuring, for the first time, the vibrational temperatures of CO 2 and the CO and CO 2 concentrations in realistic Martian conditions. In situ Fourier transform infrared spectroscopy measurements are performed in experiments conducted in DC glow discharges operating at pressures p = 1-5 Torr, discharge currents I = 10-50 mA, initial gas temperatures of 220 K and 300 K, both in pure CO 2 and in the synthetic Martian atmosphere 96% CO 2 -2% Ar-2% N 2 . To analyze and interpret the experimental results, we develop a detailed self-consistent kinetic model for pure CO 2 plasmas, describing the coupled electron and heavy-particle kinetics. The simulation results are in very good agreement with the experimental data. It is shown that the low-temperature conditions may enhance the degree of vibrational non-equilibrium and that the Martian atmospheric composition has a positive effect on CO 2 decomposition. Accordingly, the present investigation confirms the potential of plasma technologies for in situ resource utilization on Mars.
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