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Threefold-hollow adsorption modes

In a considerable number of cases both sets of modes have been observed in on-specular VEEL spectra, and the deduction has been made that the symmetry of the surface complex is Cs (or less) (145,146,151,152,160,162). The question remains whether this implies a twofold bridged adsorption site or a neighbor-induced asymmetry within an essentially C3 site, as already described. However, there are examples of species on Pt(lll) (150), Ni(ll 1) (117), and Cu(lll) (161) surfaces for which MSSR as applied to VEEL spectra clearly indicates C3v symmetry of the surface complex, without significant differences in the other frequencies as observed off-specular. These favorable cases may arise from particularly regular arrays of adsorbed species, the presence of which could very profitably be confirmed by LEED. We deduce that the CH3 adsorption sites are intrinsically C3v as far as the bare surface is concerned, i.e., on-top or threefold hollow in nature with the threefold axis of the CH3 group perpendicular to the surface. [Pg.217]

Laser-induced desorption via the DIET process is a structure-sensitive phenomenon. Firstly, we describe the recent results for adsorbed NO on Pt(l 1 1), since the adsorption structure of this system has been misunderstood for a long time. Adsorbed species giving rise to the 1490 cm-1 NO stretching vibrational mode had been believed to be adsorbed at bridge sites [34, 35]. Recently it has been shown that this species is adsorbed at the threefold fee hollow site. This problem was pointed at first using LEED analysis by Materer et al. [36, 37]. A similar problem is the occupation of the fee and hep threefold hollow sites in a ratio of 50/50 described by Lindsay et al. [38] on the basis of a photoelectron diffraction investigation of NO on Ni(l 1 1) at a coverage of 0.25 monolayer. [Pg.297]


See other pages where Threefold-hollow adsorption modes is mentioned: [Pg.219]    [Pg.225]    [Pg.219]    [Pg.225]    [Pg.221]    [Pg.147]    [Pg.215]    [Pg.222]    [Pg.223]    [Pg.40]    [Pg.197]    [Pg.378]    [Pg.384]   
See also in sourсe #XX -- [ Pg.225 ]




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Threefold-hollow adsorption

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