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 θi = 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.