In this paper, we study the interaction of molecular oxygen with single crystal diamond (1 1 1) and (1 1 0) surfaces using thermal-programmed desorption (TPD), electron energy loss spectroscopy (EELS) and Auger electron spectroscopy (AES). The clean diamond surfaces were prepared by an ex-situ hydrogenation of the diamond samples in hydrogen plasma followed by an in-situ thermal annealing. Reconstructed clean C(1 1 1)-(2 x 1) and C(I 10) surfaces were obtained. It was found that molecular oxygen is easily chemisorbed on the clean diamond surfaces at room temperature. Carbon monoxide was the only product of thermal desorption from both surfaces. Desorption of CO from both surfaces was found to obey first-order kinetics. Apart from a low temperature desorption peak present in all TPD spectra, two CO desorption peaks at 790 and 1030 degreesC were observed for the C(1 1 1)-(2 x 1) surface, whereas, only one desorption peak in the 760-890 degreesC range was observed in case of the C(1 1 0) surface. This CO desorption was interpreted to have resulted from thermal decomposition of bridge C-O-C and ontop C=O bonded oxygenated species formed on the topmost surface layer as a result of molecular oxygen adsorption. The activation energies and pre-exponential factors for CO desorption were determined for both C(1 1 1)-(2 x 1) and C(1 1 0) surfaces. The thermal stability of the bridge C-O-C and on-top C=O species on the diamond surfaces is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.