Excitation of the lowest CO2 vibrational states by electrons in hypersonic boundary layers

Abstract

The state-to-state vibrational kinetics of a CO2/O2/CO/C/O/e− mixture in a hypersonic boundary layer under conditions compatible with the Mars re-entry is studied. The model adopted treats three CO2 modes (the two degenerated bending modes are approximated as a unique one) as not independent ones. Vibrational-translational transitions in the bending mode, inter-mode exchanges within CO2 molecule and between molecules of different chemical species as well as dissociation-recombination reactions are considered. Attention is paid to the electron-CO2 collisions that cause transitions from the ground vibrational state, CO2(0,0,0), to the first excited ones, CO2(1,0,0), CO2(0,1,0) and CO2(0,0,1). The corresponding processes rate coefficients are obtained starting from the electron energy distribution function, calculated either as an equilibrium Boltzmann distribution at the local temperature or by solving the Boltzmann equation.Results obtained either neglecting or including in the kinetic scheme the electron-CO2 collisions are compared and explained by analysing the rate coefficients of the electron-CO2 collisions.