Atomic and molecular data for spacecraft re-entry plasmas

The modeling of atmospheric gas, interacting with the space vehicles in re-entry conditions in planetary exploration missions, requires a 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 non-equilibrium 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 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 electron-impact 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 (N2, O2, NO), Mars (CO2, CO, N2) and Jupiter (H2, He) atmospheres are considered

Total and dissociative electron-impact cross sections for X-1 Sigma(+)(g) -> B-1 Sigma(+)(u) and X-1 Sigma(+)(g) -> C-1 Pi(u) transitions of vibrationally excited tritium and deuterium-tritium molecules

Electron-impact fetal and dissociative cross sections, calculated by using the impact-parameter method, for the X(1)Sigma (+)(g) --> B(1)Sigma (+)(u) and X(1)Sigma (+)(g) --> C(1)Pi (u) transitions of vibrationally excited T-2 and DT molecules, are presented. The mass and vibrational energy scalings of these cross sections are discussed

Single electron capture in slow H-+A(3+) collisions

The cross section of single-electron capture in slow H- + A(3+) --> H + A(2+)(n) collisions is calculated in the one-electron approximation by using the close coupling approach. It is found that the change of the electronic configuration, that takes place at every avoided crossing of the ionic and covalent energy terms, is a source of nonadiabatic transitions in the system. This effect leads to a substantial increase of the total cross section and produces an effective repopulation of individual covalent states

Resonant Electron-transfer in Slow Collisions of Protons With Rydberg Hydrogen-atoms

The resonant charge-transfer reaction of protons on highly excited hydrogen atoms is considered by taking into account both the tunneling (under-barrier) and the over-barrier (classically allowed) electron transitions. It is demonstrated that in a wide range of variation of the reduced velocity v=vn, the classical transition mechanism is predominant. Cross-section calculations for principal quantum numbers n between 10 and 50 are presented. The results for 45n50 are compared with the available experimental data and with other theoretical calculations. © 1984 The American Physical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Molecular-energy Splitting of Highly Excited-states in the 2-coulomb-center Problem

With the use of the comparison-equation method, asymptotically exact analytical expressions are derived for the molecular-energy splittings of highly excited states of the one-electron two-Coulomb-center system (Z1eZ2). Both the symmetrical (Z1=Z2) and non-symmetrical (Z1Z2) cases are studied. The physical implications of our results are discussed, and their relationship with the expressions corresponding to low-lying states is analyzed. © 1982 The American Physical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

Electron capture and excitation in slow H++He*(n=3) collisions

The electron-capture and excitation processes in slow collisions of protons with He*(1s3l) are studied using the close-coupling method within the semiclassical approximation. The Stark splitting of electron-capture states on H is explicitly taken into account and the coupling-matrix elements between these states and the initial angular-momentum states on He are calculated analytically. The cross sections for excitation (de-excitation) and single-electron capture to specific spherical hydrogen states have been calculated in the relative velocity range 2 x 10(6)-1.3 x 10(8) cm s(-1). The cross section values for both types of processes in the considered velocity range are found to be large (10(-14)-10(-13) cm(2)) due to the large values of electron-exchange couplings at large internuclear distances. The excitation (de-excitation) processes are controlled by two-step exchange (capture and re-capture) transitions rather than by direct coupling among the states centred on He

Electron capture and excitation in slow H+ + He*(n) collisions

Electron capture and excitation (de-excitation) processes in slow collisions of protons with excited helium, H+ + He*(1s, NL) --> H*(nl) + He+(1s) or --> H+ + He*(1 s, N'L'), are studied by using the close coupling of the states {N, n} = 2, 3, 4 within the approach described in a previous paper. At small collision velocities, 10(6) cm s(-1) < v < 5 x 10(7) cm s(-1), the cross sections for excitation(de-excitation) are very large, due to the importance of two-step transitions. The coupling of the states with different principal quantum numbers significantly increases the cross sections for electron capture at adiabatically small collision velocities

Transfer ionization in slow H++H- collisions

The transfer ionization reaction H-a(-) + H-b(+) = H-a(+) + H-b(1s) + e, on which we had previously carried out experiments and calculations, is reconsidered here at higher collision energies and interpreted as ionization of weakly bound electron of the H- ion, accompanied by a simultaneous resonant exchange of the 1s core electron. The ionization of H- is treated as being strongly coupled to the dominant mutual neutralization channels H-a(-) + H-b(+) = H-a (1s) + H-b (nlm), and the cross sections for all relevant reaction channels are calculated by using the molecular-orbital close-coupling scheme