Chemical energy accommodation of atomic oxygen recombination on silica surfaces under high-temperature nonequilibrium flow environments: Insights from atomistic-scale simulations

The energy transfer and accommodation for the catalytic recombination of atomic oxygen (O) on silica surfaces, a key process to be understood for the accurate prediction of aerothermal heating of hypersonic vehicles, are studied using a combination of the density functional theory (DFT) and reactive molecular dynamics calculations. The key elementary reactions are determined by the DFT calculations, along with the barriers and changes of free energy for each reaction. The energy carried by the recombined oxygen molecules (O2) and its partition into different internal modes for various reactions are obtained by averaging the corresponding molecular information from a significant number of molecular dynamics trajectories. The chemical energy accommodation (CEA) coefficients, for various reactions, internal modes, and surface structures, are then computed based on the free energy changes and energies carried by the recombined O2. Moreover, the detailed energy distributions of O2 are also provided. It is found that CEA for the recombination of O on the silica surfaces depends greatly on the reaction type and internal energy mode but is less profoundly influenced by the surface structures. The results of the present study offer better insights into the mechanisms of chemical energy transfer and accommodation for the catalytic recombination of O on silica surfaces and can help improve the modeling of the relevant gas–surface interactions for more reliable aerothermal heating prediction.