A study of the core-electron X-ray photoelectron (X-p.e.) spectra of the f o compounds La, O, , LaMO, (M = Fe and Co), CeO,. and BaCeO, is described. Results on the chelate species [La(tmhd),] and [Ce(tmhd),] (tmhd = 2,2,6,6-tetramethylheptane-3,5-dionato) are included for comparison. Special precautions have been taken to ensure an optimal degree of surface purity of the samples. Satellite structure has been observed for the 4p. in addition to the 3d and 4d, signals in both the lanthanum(iii) and cerium(iv) compounds. These satellites are discussed in terms of coexcitations of the charge-transfer type, principally 0 2p + metal 4f transitions. In the cerium(1v) oxides the satellites are apparently due to energy-gain (representing ' shake-down ') rather than energy-

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Scanning tunneling microscopy and core level photoelectron spectroscopy measurements have been used to investigate the morphology of ZnO(0001 macro)-O, and its reactivity with carbon monoxide and carbon dioxide, as a function of surface preparation. Real space images of the surface indicate that increasing the substrate anneal temperature during preparation significantly reduces the surface step density. Surface defect concentration is also monitored by employing formic acid as a chemical probe, which is shown to adsorb dissociatively (HCOOH --> [HCOO](-) + H(+)) only on zinc cations at step edges. Carbon 1s X-ray photoelectron spectra show that carbon monoxide and carbon dioxide both react to form surface carbonate species. Spectra, recorded both as a function of surface preparation and following coadsorption, demonstrate that the carbonate formed from either reactant molecule is located at oxygen vacancies at step edges, evidencing the significant role that defects can play in the surface chemistry of ZnO(0001 macro)-O.

The partial cross-section and asymmetry parameters of the 2 s 1 , 2 A 1 and 2 B 2 ionic states of H 2 o+ have been measured at photon energies of 18-31 eV, by time-of-flight photoelectron spectroscopy using synchrotron radiation. The atomic character of the molecular orbitals is discussed in the interpretation of similarities and differences between the measurements for these states. Other synchrotron radiation data, resonance line measurements, and (e,2e) dipole results are ineluded. A multiple-scattering Xa (MSXa) calculation and a ground-state inversion method calculation are in good agreement with our crosssection measurements. There is excellent agreement between experimental asymmetry parameters and those computed from the MSXa method.Stieltjes-Tchebycheff imaging model calculations suggest the presence of resonant channels. This may be the origin of weak resonance structure present in the measurements.