We have utilized oxygen-modified C/Mo(110) surfaces as model systems to determine the modification effect of oxygen in "oxycarbides." Using cyclohexene, ethylene, and methanol as probe molecules, we observed that the reactivity of the O/C/Mo(110) surfaces depended strongly on the temperature at which oxygen was introduced onto the C/Mo(110) surface. The reaction pathways were determined using both temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). For example, the O/C/Mo(110) surface obtained by exposing the carbide surface to oxygen at 600 K became chemically inert toward all three molecules. On the other hand, the 900 K O/C/Mo(110) surface was active toward all three molecules, and for the most part retained the Pt-like reaction pathways observed on unmodified C/Mo(110). Furthermore, we have also compared the electronic properties of the O/C/Mo(110) surfaces using two synchrotron spectroscopies, soft X-ray photoelectron spectroscopy (SXPS) and near-edge X-ray absorption fine structure (NEXAFS); the results revealed similar electronic properties between the 900 K O/C/Mo(110) and unmodified C/Mo(110) surfaces. (C) 2004 Elsevier Inc. All rights reserved.