Dissociative adsorption of oxygen on Ru(0 0 0 1) surface was investigated by supersonic molecular beam method combined with high resolution X-ray photoelectron spectroscopy (XPS) using synchrotron radiation. We examined the effects of molecular vibrational excitation as well as translational energy on dissociative adsorption of oxygen in the direct adsorption regime. We found an enhancement of dissociative oxygen adsorption on Ru(0 0 0 1) by molecular vibrational excitation, indicating that potential energy surface has a late barrier for this system. (c) 2006 Elsevier B.V. All rights reserved.