Quantum chemical prediction of reaction pathways and rate constants for the reactions of O _x (x = 1 and 2) with pristine and defective graphite (0001) surfaces

We present reaction pathways for adsorption reactions of the O atom and O ₂ molecule in the pristine and monovacancy defective graphite (0001) based on quantum chemical potential energy surfaces (PESs) obtained by the dispersion-augmented density-functional tight-binding (DFTB-D) method. We use a dicircumcoronene C ₉₆H ₂₄ (L0D) graphene slab as the pristine graphite (0001) model and dicircumcoronene C ₉₅H ₂₄ (LIV) as the graphite (0001) monovacancy defect model. We found that the adsorption reactions of O and O ₂ on the L0D surface can produce defects on the graphite surface. O can yield CO, while O ₂ can yield both CO and CO ₂ molecules. The adsorption reactions of the O and O ₂ on the LIV surface can produce a 2-C defective graphite surface and CO, and CO and CO ₂, respectively. The O and O ₂ more readily oxidize the defected surface, LIV, than the defect-free surface, L0D. On the basis of the computed reaction pathways, we predict reaction rate constants in the temperature range between 300 and 3000 K using Rice-Ramsperger-Kassel- Marcus (RRKM) theory. High-temperature quantum chemical molecular dynamics simulations at 3000 K based on on-the-fly DFTB-D energies and gradients support the results of our PES studies.