Monte Carlo model of electron energy degradation in a CO2 atmosphere

TL;DR

This paper presents a Monte Carlo model for electron energy degradation in CO2 atmospheres, providing analytical yield spectra, efficiencies, and secondary electron distributions relevant for planetary atmospheres like Mars and Venus.

Contribution

The study introduces an analytical yield spectra model for electron degradation in CO2, including detailed cross sections, efficiencies, and secondary electron distributions, advancing understanding of atmospheric electron processes.

Findings

Mean energy per ion pair: 37.5 eV at 200 eV, 35.8 eV at 1000 eV

Ionization accounts for ~50% of energy loss above 50 eV

Dominant excitation states at ~13.6 eV and 12.4 eV contribute significantly to energy loss

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' 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 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 (AYS). We have calculated the mean energy per ion pair and efficiencies for various inelastic processes, including the double and dissociative double ionization of \car\ 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 experimental value 32.7 eV at high energies. Ionization is the dominant loss process at energies above 50 eV with 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.