Monte Carlo model of electron energy degradation in a CO₂ atmosphere

Abstract

A Monte Carlo model has been developed to study the degradation of ≤1000 eV electrons in an atmosphere of CO₂, which is one of the most abundant species in Mars' and Venus's atmospheres. The e-CO₂ cross sections are presented in an assembled set along with their analytical representations. Monte Carlo simulations are carried out at several energies to calculate the "yield spectra", which embodied all the information related to the electron degradation process and can be used to calculate "yield" (or population) for any inelastic process. The numerical yield spectra have been fitted analytically, resulting in an analytical yield spectra. We have calculated the mean energy per ion pair and efficiencies for various inelastic processes, including the double and dissociative double ionization of CO₂ and negative ion formation. The energy distribution of the secondary electrons produced per incident electron is also presented at few incident energies. The mean energy per ion pair for CO₂ is 37.5 (35.8) eV at 200 (1000) eV, compared to the experimental value 32.7 eV at high energies. Ionization is the dominant loss process at energies above 50 eV with a contribution of ~50%. Among the excitation processes, 13.6 eV and 12.4 eV states are the dominant loss processes consuming ~28% energy above 200 eV. Around and below ionization threshold, 13.6 eV, 12.4 eV, and 11.1 eV, followed by 8.6 eV and 9.3 eV, excitation states are important loss processes, while below 10 eV, vibrational excitation dominates.