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Angle-resolved photoemission spectra of the (100) and (110) faces of Ti02 have been recorded in the photon-energy range from 18 to 47 eV. These normal emission data have been analyzed on the basis of direct transitions into free-electron-like final states, yielding valence-band dispersion relations, E(k), along the high-symmetry 5 and X lines of the bulk Brillouin zone. Polarization selection rules are derived for the appropriate nonsymmorphic space group, which are used to identify the symmetries of the valence bands. Empirical dispersion relations are compared with the results of a band-structure calculation, which employed an ab initio atomic orbital-based method. While there is reasonable agreement overall, for a 6-line empirical band at about 1.2 eV below the valence-band maximum (E"& ) there is no counterpart in the calculated bulk band structure. This discrepancy may be related to a Ti02(100) surface resonance predicted to lie 1.5 eV below E"& .

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Surface EXAFS, NEXAFS and photoemission have been used to study the structure of surface phases resulting from reaction of H,S with NiO( 100) a n d SO2 with TiO,( 110). S K-edge SEXAFS data, in conjunction with the L E E D pattern symmetry, suggest that the NiO( 100)/H2S reaction at 570 K results in reduction of the substrate to form a n azimuthally aligned Ni( 100)c(2 x 2 ) s raft, with S occupying the fourfold Ni( 100) hollow site. S K-edge NEXAFS results for SO, adsorption on low-temperature TiO,( 110) identify two surface SO, species: chemisorbed SO, and SO:-. The polarisation dependence of the NEXAFS suggests that the SO2 molecular plane lies close to parallel t o the surface. Photoemission data also evidence chemisorption at 110 K and show that this precursor phase reacts further in a thermally activated process to form a stable surface sulphate-like species. A mechanism is suggested which involves SO, bonding to a terrace Ti site, with a n activated h o p t o a n adjacent site in which sulphur bonds to two oxygen atoms on the raised row.

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