Using ultraviolet photoelectron spectroscopy (UPS), temperature programmed desorption (TPD), and periodic density functional theory (DFT), we have investigated the oxidation chemistry of diamond (111) surface following its exposure to atomic oxygen generated from a remote radio frequency discharge. Partial O uptake occurs on the C(111) 2 x 1 surface at room temperature without lifting the surface reconstruction. A 2 x 1 --> 1 x 1 transition and a full monolayer O coverage is only achieved following the oxygenation of the diamond surface at elevated temperatures (400 degreesC). Exchange of chemisorbed D by atomic O, and vice versa, is facile at room temperature. Desorption products originating from the reaction chemistry between O and D such as D2O were observed on the C(111) surface in addition to CO. The C(l 11) surface is readily graphitized following the desorption of CO from the surface. In addition, the structure and energetic,, of oxygenated C(111) 1 x 1 and C(111) 2 x 1 surfaces have been studied using periodic density functional theory (DFT). The oxidation processes have been examined in terms of the reaction heats. The calculations revealed that the epoxy configuration formed by bridging O on the Pandey chain is more stable at low O coverage, these converted to a carbonyl-type oxygen species at higher coverages. Reaction heat considerations suggest that hydroxyl-terminated C(111) 1 x 1 may be the final stable product in the presence of atomic hydrogen.