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.

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(0001) and Cr 2 O 3 (0001) surfaces based on low energy electron and surface X-ray diffraction methods. However, the PhD investigation fails to provide definitive evidence for the presence or absence of surface vanadyl (V=O) species associated with atop O atoms on the surface layer of V atoms. Specifically, the best-fit structure does not include these vanadyl species, although an alternative model with similar relaxations but including vanadyl O atoms yields a reliability-factor within the variance of that of the best-fit structure.keywords: surface relaxation; surface structure; vanadium oxide; photoelectron diffraction  present address:

Scanned-energy mode photoelectron diffraction results show the adsorption site of molecular water on TiO2(110) to be atop under-coordinated surface Ti atoms, confirming the results of total energy calculations and STM imaging. However, the Ti-O(water) bond length is 2.21 +/- 0.02 A, much longer than Ti-O bond lengths in strongly chemisorbed species on this surface, but significantly shorter than found in most total energy calculations. The need for theory to describe this weak bond effectively may be a key factor in the controversial problem of understanding this important surface reaction system.

Using high-resolution core-level photoelectron spectroscopy and modified Anderson impurity model calculations, we study the Mn 2p spectrum of manganese metal and resolve the current debate about its spectral shape. An unusual satellite feature, 1 eV from the main peak, is observed in the Mn 2p 3/2 spectrum of a thick Mn layer grown on Al. It originates from intra-atomic multiplet effect related to Mn atoms with large local moment. The satellite decreases in intensity for thin Mn layers and for Al deposition on bulklike Mn because of enhanced Mn 3d hybridization with Al s , p bandlike states. The reason for the absence of a charge-transfer satellite is discussed.

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The results of experimental measurements and theoretical simulations of circular dichroism in the angular dependence (CDAD) of photoemission from atomic core levels of each of the enantiomers of a chiral molecule, alanine, adsorbed on Cu(110) are presented. Measurements in, and out of, substrate mirror planes distinguish CDAD due to the chirality of the sample and the experimental geometry. The effect due to sample chirality is relatively weak, so such measurements may not provide a routine spectral fingerprint of adsorbate chirality. DOI: 10.1103/PhysRevLett.92.236103 PACS numbers: 68.43.Fg, 33.55.Ad, 79.60.Dp There has been growing interest in the last few years in the properties of chiral molecules adsorbed on surfaces (e.g., [1][2][3][4][5][6]), motivated in part by the potential importance of producing molecular products of a single ''handedness'' (enantioselective) by heterogeneous catalysis. In such studies a simple spectroscopic measurement, which could establish if the surface species (which may be unknown reaction intermediates) are predominantly of a single chirality, would be of great value. Conventional optical absorption measurements on submonolayer coverages of adsorbed molecules which exploit the circular dichroism (a difference in absorption for left-and rightcircularly polarized radiation) are unlikely to be fruitful. However, spatially oriented chiral molecules, such as those adsorbed on a surface, should show circular dichroism in the angular distribution (CDAD) of photoelectrons emitted from these species [7,8]. Indeed, such an effect has recently been observed [9] even for randomly oriented chiral molecules in the gas phase. Here we present the results of experiments, and model calculations, which evaluate this idea using core level photoemission from one model system, alanine on Cu(110); our results confirm the existence of the effect but show it is weak relative to other sources of CDAD unrelated to the surface chirality, casting doubt on the likely utility of this phenomenon to provide a routine spectral fingerprint.We chose core level photoemission for these CDAD studies because the elemental and chemical-state specificity offered by photoelectron binding energies allows one to localize the information on chirality to specific adsorbed species on a surface; this is not true for photoemission from the valence states in which contributions from substrate and coexistent adsorbed species generally overlap. An important aspect of CDAD, however, is that even nonchiral surfaces give rise to a significant signal if the geometry of the experiment is chiral [10]. If the plane defined by the incident (circularly polarized) light and the photoelectron collection direction does not correspond to a mirror symmetry plane of the sample, the experiments conducted with opposite circular polarizations will not be equivalent and so a circular dichroism signal will be observed. This CDAD effect (up to 50% or more) from core levels of atoms in nonchiral surfaces is well established from substrate atoms [...

Scanned-energy mode C 1s photoelectron diffraction has been used to investigate the local adsorption geometry of benzene on Si(001) at saturation coverage and room temperature. The results show that two different local bonding geometries coexist, namely the 'standard butterfly' (SB) and 'tilted bridge' (TB) forms, with a composition of 58 ± 29% of the SB species. Detailed structural parameter values are presented for both species including Si-C bond lengths. On the basis of published measurements of the rate of conversion of the SB to the TB form on this surface, we estimate that the timescale of our experiment is sufficient for achieving equilibrium, and in this case our results indicate that the difference in the Gibbs free energy of adsorption, G(TB) − G(SB), is in the range −0.023 to +0.049 eV. We suggest, however, that the relative concentration of the two species may also be influenced by a combination of steric effects influencing the kinetics, and a sensitivity of the adsorption energies of the adsorbed SB and TB forms to the nature of the surrounding benzene molecules.