A General Analytic Electron-Impact Ionization Electron Energy Sharing Model for Monte Carlo Plasma and Swarm Applications

Modeling non-equilibrium plasmas or swarm experiments with Monte Carlo collision codes or Boltzmann equation solver codes requires input of comprehensive sets of collision cross sections and or scattering models. Of particular interest are the scattering models utilized for the ionization process, where detailed angle and energy resolved cross sections are generally not available in the literature.

Recently we have developed a general analytic model for calculating the electron-impact ionization electron energy sharing distribution function, which can be readily implemented in Monte Carlo simulation codes. Here we present our approach and show the utility of the model for a range of impact energies, species, ions, and excited states, by comparing the analytic model to accurate close-coupling and distorted-wave scattering calculations. We compare this approach to scattering models generally utilized by Boltzmann equation solver and collisional Monte Carlo codes, e.g. the commonly used model of C. B. Opal et al. J. Chem. Phys. 55, 4100 (1971), the equal-energy sharing approximation, and approximating the primary electron to take all of the excess energy. We note that unlike the commonly used approach of Opal, the present analytic model is applicable to all species, requires minimal input data from the user, and does not rely on experimentally determined parameters.