Migration of Hydroxyl on Diamond(001)-2 × 1 Catalyzed by Gaseous Water: A Density Functional Theory Study

Density functional theory simulations were used to examine the effect of the presence of gaseous water, H2O(g), on the migration dynamics of a chemisorbed hydroxyl, OH(ad), on diamond(001)-2 × 1. We show that the molecular adsorption of H2O(g) is enhanced in the presence of OH(ad), forming a variety of hydrogen-bonded complexes, H2O···OH(ad), on diamond(001)-2 × 1, as revealed by the analysis of projected density of states, partial charge density, normal modes of vibration, and heats of adsorption. Remarkably, the internal dissociation of the captured water causes a series of concerted motions of the hydrogen-bonded complexes and the underlying substrate atoms, from which the fragment of hydroxyl from dissociation is deposited onto an adjacent surface site to form a new hydroxyl chemisorbed on diamond(001)-2 × 1. Meanwhile, the other dissociation fragment of atomic hydrogen abstracts the prior chemisorbed hydroxyl to reform a water molecule that readily participates in the next iteration of molecular adsorption and subsequent internal dissociation when interacting with the newly formed hydroxyl. Effectively, this process represents the gaseous water-catalyzed migration of a surface hydroxyl on diamond(001)-2 × 1 in a self-repeating fashion, exhibiting an isotropic barrier of 0.32 eV regardless of the migration direction. These findings are in contrast to the anisotropic migration of hydroxyl on diamond(001)-2 × 1 in the absence of gaseous water, in which the barriers were computed as 1.96 eV along [11̅0] and 2.24 eV along [110].