First principles calculations of the chemisorption properties of nitro-containing molecules on the Al₂O₃(0001) surface

First-principles calculations based on density functional theory (DFT) and the generalized gradient approximation (GGA) have been used to study the adsorption of nitromethane (NM) and 1,1-diamino-2,2-dinitroethylene (FOX7) molecules on the basal plane of α-Al₂O₃ crystal. The calculations employ a (2×2) supercell slab model and 3D periodic boundary conditions. Based on these calculations we have determined that both NM and FOX7 molecules can adsorb nondissociatively on the surface, with the most stable adsorption configurations parallel to the surface. The corresponding binding energies are found in the range 25.3-26.0 kcal/mol for NM and 35.6-48.3 kcal/mol for FOX7 depending on the relative molecular orientation and the corresponding surface sites. The minimum energy pathways for NM dissociation have been determined and a low energy pathway leading to H elimination with formation of adsorbed CH₂NO₂ and hydroxyl species has been identified. Additional calculations have focused on adsorption properties of aci-nitromethane tautomers and on description of the energetic pathways connecting adsorbed nitromethane molecule with these tautomers.