Geant4-DNA development for atmospheric applications: N2, O2 and CO2 models implementation

Background and aim: Cosmic rays have the potential to induce significant changes in atmospheric chemical reactions by generating ions, thereby influencing the atmosphere's chemical composition. The use of particle–molecule interaction models that account for the molecular structure of the atmospheric medium can advance our understanding on the role of ions, and enables a quantitative analysis of the impact of ion-molecule reactions on atmospheric modifications. This study marks the initial effort to expand the Geant-DNA toolkit for atmospheric applications. Methods: Building on our previous work, we extended the validation of new electron impact interaction models with the nitrogen and oxygen molecules up to 10 MeV. Additionally, we introduce electron cross sections for the carbon dioxide molecule, due to its crucial role as a major greenhouse gas. We present the implementation of the cross section models in Geant4-DNA, along with their validation through simulations of stopping power and range. Results: The differential cross sections have been verified against analytical calculations, demonstrating good agreement with existing literature data for all three molecules. The implementation has been validated through simulations of stopping power and range in N2, O2, CO2, and air. Results demonstrate agreement within 6% compared to reference data from the ESTAR database. Conclusions: The cross section models for the N2, O2, and CO2 atmospheric molecules have been implemented in the Geant4-DNA toolkit. This evolution is crucial for studying ionic reactive chemical networks in a quantitative manner, assessing the impact of ionization on chemical reactions occurring in the atmosphere and their implications for climate.