Rarefied and hypersonic gas flows involve strongly non-equilibrium conditions in which energy transfer between translational, rotational, and vibrational degrees of freedom governs chemical reactivity. To investigate these processes at a microscopic level, quasi-classical trajectory simulations were performed for the O + O₂[1], N + O₂[2], and N + NO[3] collision systems on full-dimensional reactive potential energy surfaces(PES) based on high-level electronic structure calculations. The full state space was characterized by analysing elastic, inelastic, atom-exchange, reactive, and atomisation channels over a broad range of initial rovibrational states. Distinct structure–reactivity relationships emerge from the simulations: low rovibrational excitation predominantly leads to elastic and inelastic scattering, rotational excitation enhances atom-exchange reactivity, and strong vibrational excitation promotes atomisation and complete dissociation. Final-state probability maps reveal significant vibrational-to-rotational energy redistribution during reactive collisions and highlight how different regions of the initial state space contribute to specific reaction outcomes. For the O + O₂ system, two independently developed reactive PES based on Reproducing Kernel Hilbert Space(RKHS)[4] and permutationally invariant polynomials(PIPs)[5,6]  representations yield consistent state-resolved dynamics despite their different electronic-structure methodologies, demonstrating the robustness of the predicted trends. These results provide a comprehensive state-space description of energy flow in atom–diatom collisions relevant to hypersonic chemistry and offer a foundation for future state-specific and data-driven models of non-equilibrium gas dynamics.

[1] J. Jang, J. C. S. V. Veliz, M. Upadhyay, M. Meuwly, J. Chem. Phys., 2025, 163, 074109.

[2] J. C. San Vicente Veliz, D. Koner, M. Schwilk, R. J. Bemish, M. Meuwly, Phys. Chem. Chem. Phys., 2020, 22, 3927-3939.

[3] D. Koner, J. C. San Vicente Veliz, R. J. Bemish, M. Meuwly, Phys. Chem. Chem. Phys., 2020, 22, 18488-18498.

[4] O. T. Unke, M. Meuwly, J. Chem. Inf. Model., 2017, 57, 1923-1931.

[5] B. Jiang, J. Li, H. Guo, Int. Rev. Phys. Chem., 2016, 35, 479-506.

[6] Z. Varga, Y. Paukku, D. G. Truhlar, J. Chem. Phys., 2017, 147, 154312.