CO dissociation on Mo(110) studied by high-resolution core-level spectroscopy

We have studied the CO/Mo(1 1 0) adsorption system at different sample temp eratures by high-resolution core-level spectroscopy and near-edge X-ray-abs orption fine-structure measurements. We demonstrate that CO molecules havin g different tilt angles with respect to the surface normal may be assigned to different components of the C Is core-level spectra. The tilt of the CO molecules is shown to depend on the CO coverage. The thermally induced diss ociation of CO is studied and is shown to differ at low and high initial CO coverages. At low coverage CO dissociation starts already at temperatures as low as 125 K whereas at saturation CO coverage no dissociation occurs be low 280 K. The reasons for this difference in dissociation behavior are dis cussed and it is concluded that steric effects play a large role. (C) 2001 Elsevier Science B.V. All rights reserved.