Molecular Physics of Elementary Processes Relevant to Hypersonics: Electron-Molecule Collisions

Plasma Sources Sci. Technol.

Armenise

Cacciatore

et al. 2016

The modeling of atmospheric gas, interacting with the space vehicles in re-entry conditions in planetary exploration missions, requires large set of scattering data for all those elementary processes occurring in the system. A fundamental aspect of re-entry problems is represented by the strong nonequilibrium conditions met in the atmospheric plasma close to the surface of the thermal shield, where numerous interconnected relaxation processes determine the evolution of the gaseous system towards the equilibrium conditions. A central role is played by the vibrational exchanges of energy, so that collisional processes involving vibrationally excited molecules assume a particular importance. In the present paper, theoretical calculations of complete sets of vibrationally state-resolved cross sections and rate coefficients are reviewed, focusing on the relevant classes of collisional processes: resonant and non-resonant electronimpact excitation of molecules, atom-diatom and molecule-molecule collisions as well as gas-surface interaction. In particular, collisional processes involving atomic and molecular species, relevant to Earth (N 2 ,O 2 ,NO), Mars (CO 2 ,CO,N 2) and Jupiter (H 2 ,He) atmospheres are considered.

Section: The Prototypical Case Of Co 2 Plasmasmentioning

confidence: 99%

Atomic and molecular data for spacecraft re-entry plasmas

Plasma Sources Sci. Technol.

Armenise

Cacciatore

et al. 2016

“…This implies that the scattering processes involves one mode only and does not affect at all the other two. Preliminary results for the symmetric stretch mode only, were given previously [19]. Here we present calculations on all the three normal modes of the molecule, for 0 ≤ ν i ≤ ν ′ i ≤ 10 (i = 1, 2, 3), and for electron collision energies from the threshold up to 10 eV.…”

mentioning

confidence: 92%

“…The resonant cross section for the process in (1) of a single normal mode ν has been calculated [16,19,21], as a function of the electron energy ǫ, by:…”

mentioning

confidence: 99%

Calculated low-energy electron-impact vibrational excitation cross sections for CO₂molecule

Laporta

Tennyson

Plasma Sources Sci. Technol.

2016

Vibrational-excitation cross sections of ground electronic state of carbon dioxide molecule by electron-impact through the CO − 2 ( 2 Π u ) shape resonance is considered in the separation of the normal modes approximation. Resonance curves and widths are computed for each vibrational mode. The calculations assume decoupling between normal modes and employ the local complex potential model for the treatment of the nuclear dynamics, usually adopted for the electron-scattering involving diatomic molecules. Results are presented for excitation up to 10 vibrational levels in each mode and comparison with data present in the literature is discussed.One of the technological problems, connected with strategies for reduction of the global warming coming from the greenhouse effect produced by carbon dioxide, is represented by the capture at source and storage of the CO 2 gas, mainly based on the plasmolysis process leading to the splitting of CO 2 into CO molecules and atomic or molecular oxygen [1,2]. The efficiency of the dissociation processes is strongly determined by the vibrational activation of the molecule. Models of CO 2 plasmas, aimed to optimize and clarify this chemical conversion, have recently been constructed [3][4][5][6][7]. The main limitation of these models is the lack of information on electron-impact cross sections or rate coefficients for collisions inducing vibrational transitions in CO 2 molecules; as result modellers usually resort to estimated rates or approximate scaling-laws [6].In order to fill this void, in this Letter we present a preliminary data set of electronimpact cross sections for vibrational excitation of ground electronic state of carbon dioxide molecule useful in plasma kinetic modeling. The cross sections show two distinctive features observed experimentally: a 2 Π u shape resonance around 3.8 eV [8][9][10] and, at energies below 2 eV, an enhancement due to the presence of the 2 Σ + g symmetry virtual state [11][12][13]. Both phenomena are explained in terms of a temporary CO − 2 system. For a general review on this topics see Itikawa paper [14] and references therein.We present here the cross sections for the following process:which occurs through the formation of the shape resonance generated by the electronic state 2 Π u of the CO − 2 ion. CO 2 in its ground electronic state, X 1 Σ + g , is a linear molecule with C-O equilibrium distance R eq = 2.19 a 0 characterized by three normal modes of vibration, denoted in the following by v = (ν 1 , ν 2 , ν 3 ) and referred to, respectively, as the symmetric stretching, bending mode (doubly degenerate) and asymmetric stretching. * vincenzo

“…Potential curves for CO 2 and CO − 2 and widths were obtained by ab initio calculations [18]. In Fig.…”

Section: Figurementioning

confidence: 99%

Electron collisions with excited molecules in low temperature plasmas

Laporta

2015

EPJ Web of Conferences