Using chemical-state-specific scanned-energy-mode photoelectron diffraction (PhD) from O 1s and C 1s photoemission, we have determined the local structure of the surface species produced on the rutile TiO 2 (110) surface as a result of room temperature exposure to formic acid. The results show clear evidence for the coexistence of formate, HCOO, and hydroxyl, OH, surface species. The formate species is aligned along [001], bridging an adjacent pair of surface 5-fold-coordinated Ti atoms with the formate O atoms nearly atop the Ti atoms with a Ti-O bond length of 2.08 ( 0.03 Å, consistent with scanning tunneling microscopy observations, a number of theoretical calculations, and an earlier very restricted PhD study. The hydroxyl species are formed by H attachment to the surface bridging O atoms and have a Ti-O bond length of 2.02 ( 0.05 Å, significantly longer than for the bridging oxygen atoms on a bulk-terminated surface or as previously reported for the clean surface. Our results exclude the possibility of a large (1/3) fractional occupation by the formate species of a second site azimuthally rotated by 90°and bonded to a surface oxygen vacancy site, as proposed in some earlier infrared and X-ray absorption spectroscopic studies. A much smaller concentration of such a second species cannot be excluded.

An ultrathin film with a periodic interlayer spacing was grown by the deposition of Cu atoms on the fivefold surface of the icosahedral Al70Pd21Mn9 quasicrystal. For coverages from 5 to 25 monolayers, a distinctive quasiperiodic low-energy electron diffraction pattern is observed. Scanning tunneling microscopy images show that the in-plane structure comprises rows having separations of S=4.5+/-0.2 A and L=7.3+/-0.3 A, whose ratio equals tau=1.618... within experimental error. The sequences of such row separations form segments of terms of the Fibonacci sequence, indicative of the formation of a pseudomorphic Cu film.

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New O 1s and N 1s scanned-energy mode photoelectron diffraction (PhD) measurements and low energy electron diffraction observations from the Cu(100)(2×4)pg phase formed by deprotonated glycine, glycinate (NH₂CH₂COO–) have been used to determine the local structure of this adsorbed phase. The favored model involves bonding of both O atoms of the carboxylate and the N atom of the amino group in near atop sites with Cu–N and Cu–O distances of 2.05 Å. This bonding geometry is similar to that of glycinate on Cu(110), but in this case the fact that the C–C backbone is aligned along (100) straggling the more widely spaced Cu atoms rows leads to a larger offset from atop of the O atoms. A reanalysis of O 1s PhD data from the Cu(110)(3×2)pg-glycinate surface shows that the two O atoms are inequivalent, with one O being offset by 0.29 Å more than the other, leading to a twist of the molecule. The results are discussed in the light of other measurements on these surfaces and recent theoretical total energy calculations, in order to obtain models of the long-range ordered phases. These favor models for both surfaces involving only heterochiral structures in which the unit mesh contains one glycinate species with each chirality, defined by the side of the C–C backbone on which the amino group bonds to the surface

Molecular photofragmentation has been studied by event imaging on HeH+ ions at 32 nm (38.7 eV) in a fast ion beam crossed with the free-electron laser in Hamburg (FLASH), analyzing neutral He product directions and energies. Fragmentation into He(1snl,n > or = 2)+H+ was observed to yield significant photodissociation at 32 nm with an absolute cross section of (1.4+/-0.7) x 10(-18) cm2, releasing energies of 10-20 eV. A clear dominance of photodissociation perpendicular to the laser polarization was found in contrast to the excitation paths so far emphasized in theoretical studies.

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New experimental structure determinations for molecular adsorbates on NiO(100) reveal much shorter Ni-C and Ni-N bond lengths for adsorbed CO and NH3 as well as NO (2.07, 1.88, 2.07 A) than previously computed theoretical values, with discrepancies up to 0.79 A, highlighting a major weakness of current theoretical descriptions of oxide-molecule bonding. Comparisons with experimentally determined bond lengths of the same species adsorbed atop Ni on metallic Ni(111) show values on the oxide surface that are consistently larger (0.1-0.3 A) than on the metal, indicating somewhat weaker bonding.