Multiple internal reflection infrared spectroscopy (MIRIRS) and temperature-programmed desorption (TPD) were used to investigate the interaction of oxygen with a diamond (110)-oriented surface. Exposure of the hydrogen-free diamond surface at 90 K to room-temperature O-2 or thermally excited oxygen, O-2* (produced with a heated iridium filament) resulted in a sharp infrared absorption at 657 cm(-1), which disappeared on heating to 300 K. The 657 cm(-1) absorption may indicate a surface peroxide. When the hydrogen-free diamond surface was dosed with O-2 at room temperature, no oxygen adsorption was observed by Auger electron spectroscopy (AES) or TPD. In contrast, dosing the surface with O-2* at 300 K led to oxygen chemisorption. The room-temperature diamond surface was saturated with oxygen after exposures of > 2400 L O-2*. When the oxidized surface was heated, only CO2 and CO desorption were observed, with peak maxima at 780 and 870 K, respectively. The peak desorption temperatures for CO2 and CO did not vary with O coverage, implying first-order desorption kinetics, MIRIR spectra of the oxygen-saturated (110)-oriented surface showed weak absorption modes at 790 and 980 cm(-1). The exposure of the surface at 900 K to O-2* led to (1) an increase in the coverage of oxygen species stable at high-temperature, (2) narrower, more intense, MIRIRS absorption modes (O-16, 770, 934, and 980 cm(-1); O-18, 747, 895, and 936 cm(-1)) and (3) a sharp, intense CO desorption peak at 1025 K. These observations imply that the low-temperature adsorption sites were etched away, thus favoring the additional adsorption of oxygen into the adsorption sites that are stable at high temperature.