Molecular vibrations in core-ionised CO adsorbed on Co(0001) and Rh(100)

Previous studies of CO on Ni(1 0 0) by Fohlisch et al. [Phys. Rev. Lett. 81 (1998) 1730] have shown that the intramolecular stretch vibration mode observed in the C Is photoelectron tines depends strongly on the chemical state of the adsorbate. In the current investigation analogous analyses have been done for CO on Co(0 0 0 1) and Rh(1 0 0). CO adsorbs in on-top sites on Co(0 0 0 1) resulting in a vibrational splitting of (210 +/- 3) meV from the adiabatic C 1s peak. Including the measured intensities and comparing with similar data from electron energy loss spectroscopy experiments the change in the equilibrium distance between the initial state and the ionised state has been deduced to be (4.2 +/- 0.2) pm. For CO on Rh(1 0 0) two adsorption sites, on-top and bridge, are populated. Similar analysis of the vibrational fine structure gives a vibrational splitting of (221 +/- 4) meV for the on-top site and (174 +/- 11) meV for the bridge site. The respective changes in the equilibrium distances are (3.8 +/- 0.2) and (5.6 +/- 0.3) pm. These results are compared with available data in literature. (C) 2001 Elsevier Science B.V. All rights reserved.