Nonequilibrium effects are critical in Mars atmospheric entry and other applications, such as CO2 lasers and in situ oxygen production on Mars. This study investigates the nonequilibrium evolution of CO2 system using a detailed state-to-state model. First, a complete kinetic scheme comprising 8625 pseudo-species is established, including 3B2 electronically excited state of CO2, with rate coefficients updated and extended using the forced harmonic oscillator model. The scheme is validated against experimental relaxation data for a pure CO2 system, showing good agreement. Subsequently, adiabatic relaxation processes are simulated for three typical states corresponding to selected Mars entry trajectory points. The nonequilibrium evolution and dominant mechanisms are analyzed in depth. The results indicate that (1) when chemical reactions are negligible, the relaxation is dominated by the vibration-translation energy transfer in the bending mode (VT2) and energy redistribution of intramode vibration–vibration transitions (VVmk), with the bending mode playing the key role; (2) under conditions when significant chemical reactions occur, the evolution processes can be divided into three stages: rapid thermal relaxation, chemical reaction incubation, and rapid chemical reaction. The incubation period bridges thermal relaxation with rapid chemistry and greatly influences the overall nonequilibrium process. Three chemical reactions, including CO2 dissociation, CO2-O exchange, and O2 dissociation, form the core reaction chain driving the system toward thermochemical equilibrium. Additionally, the impact of vibration-electronic transition on energy transfer and CO2 dissociation is relatively limited for present conditions, due to the overall low population of the 3B2 state.
Duan et al. (Fri,) studied this question.