Chemical Dynamics Simulations and Scattering Experiments for O₂ Collisions with Graphite

Energy transfer in collisions of O₂ with a graphite surface was studied by chemical dynamics simulations. The simulations were performed for three collision energies E_i of 2.1, 7.4, and 15 kcal/mol, with the initial incident angle fixed at θ_i = 45°. Simulations were performed for each E_i at a surface temperature T_surf = 300 K. For the higher surface temperature of 1177 K, a simulation was only performed for E_i = 15 kcal/mol. The following properties were determined and analyzed for the O₂ + graphite collisions: (1) translational energy distributions of the scattered O₂; (2) distribution of the final polar and azimuthal angle for the scattered O₂; and (3) number of bounces of O₂ on the surface before scattering. The average energy transferred to the graphite surface and that remaining in O₂ translation, i.e., «ΔE_surf» and «E_f», exhibit a linear dependence with the initial translational energy. For the O₂ + graphite scattering, the physisorption/desorption residence time distribution decays exponentially, with an increase in residence time with a decrease in E_i. The rate at which the distribution decreases shows a near-linear dependence with an increase in E_i. For higher collisional energies of 7.4 and 15 kcal/mol, O₂ scattering from the surface follows a nearly quasi-trapping desorption process. However, for the lowest collision energy, it mostly follows conventional physisorption/desorption. For all of the scattering conditions considered experimentally, the relationship between the average final translational energy and average scattering angle for the O₂ molecules found from the simulations is in excellent agreement with the experimental results. This experimental validation of precise simulation outcomes is important as it indicates that collisional energy-transfer predictions for this system can be reliably used in assessing interfacial energy flow in a variety of technological applications, including high-performance flight systems.