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The time-dependent evolution of the energy transfer into gas heating in the afterglow of pulsed CO2 and CO2–N2 glow discharges produced in cylindrical tubes at low pressures (1–5 Torr) is theoretically investigated, by developing a self-consistent model that couples the time-dependent gas thermal balance equation with the vibrational kinetics. The modelling predictions are in good agreement with recently published experimental data on gas temperature, obtained via time-resolved in situ Fourier transform infrared spectroscopy. The cooling of the gas in the afterglow is found to be strongly dependent on the thermal conductivity and the wall temperature. It is verified that wall and volume deactivation of CO2 vibrationally excited species influences the gas heating along the afterglow, in different proportions depending on the pressure of the gas. The time-resolved contributions of each of these cooling and heating mechanisms are discussed in detail. The new results bring an additional validation of a set of mechanisms and rate coefficients for vibrationally-energy transfers previously proposed.

The implementation of in situ rotational Raman spectroscopy is realized for a pulsed glow discharge in CO2 in the mbar range and is used to study the rotational temperature and molecular number densities of CO2, CO, and O2. The polarizability anisotropy of these molecules is required for extracting number densities from the recorded spectra and is determined for incident photons of 532 nm. The spatiotemporally-resolved measurements are performed in the same reactor and at equal discharge conditions (5-10 ms on-off cycle, 50 mA plasma current, 6.7 mbar pressure) as in recently published work employing in situ Fourier transform infrared (FTIR) spectroscopy. The rotational temperature ranges from 394 to 809 K from start to end of the discharge pulse and is constant over the length of the reactor. The discharge is demonstrated to be spatially uniform in gas composition, with a CO2 conversion factor of 0.15 ± 0.02. Rotational temperatures and molecular composition agree well with the FTIR results, while the spatial uniformity confirms the assumption made for the FTIR analysis of a homogeneous medium over the line-of-sight of absorption. Furthermore, the rotational Raman spectra of CO2 are related to vibrational temperatures through the vibrationally averaged nuclear spin degeneracy, which is expressed in the intensity ratio between even and odd numbered Raman peaks. The elevation of the odd averaged degeneracy above thermal conditions agrees well with the elevation of vibrational temperatures of CO2, acquired in the FTIR study.

International audience; Herein, it is argued that Mars has nearly ideal conditions for CO 2 decomposition by non-equilibrium plasmas. It is shown that the pressure and temperature ranges in the ##IMG## [http://ej.iop.org/images/0963-0252/26/11/11LT01/psstaa8dccieqn1.gif] ∼ 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.