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 obs erved in the C Is photoelectron tines depends strongly on the chemical stat e of the adsorbate. In the current investigation analogous analyses have be en 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 th e adiabatic C 1s peak. Including the measured intensities and comparing wit h similar data from electron energy loss spectroscopy experiments the chang e in the equilibrium distance between the initial state and the ionised sta te has been deduced to be (4.2 +/- 0.2) pm. For CO on Rh(1 0 0) two adsorpt ion sites, on-top and bridge, are populated. Similar analysis of the vibrat ional fine structure gives a vibrational splitting of (221 +/- 4) meV for t he on-top site and (174 +/- 11) meV for the bridge site. The respective cha nges in the equilibrium distances are (3.8 +/- 0.2) and (5.6 +/- 0.3) pm. T hese results are compared with available data in literature. (C) 2001 Elsev ier Science B.V. All rights reserved.