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Tennessee Eastman Co., and Dow Coming Corp. for their generous support under the Presidential Young Investigator Award (Grant No. CPE-8351190). We thank Prof. C. B. Richardson of the University of Arkansas for his technical advice.

Hl value. As shown in Figure 5, the shape of the qst curve on OG-400 and OG-25 is very similar to that on OG-700, the only difference being the fact that the break point slightly shifts to higher coverage of H20 from OG-700 to OG-400 and further to OG-25. Admittedly, there is a great difference between the qst curves on OG-700 and OG-IOOO.The reason why such a difference appears can be attributed to the fact that the CO content on OG-700 is as much as those on OG-25 and OG-400, in contrast to a smaller value on OG-IOOO (Table I). Walker and Janov have reported that the CO-desorbing oxides on Graphon act as the sites for adsorption of H20, which give the heat of adsorption similar to the HL value.22 Thus, the H20 molecules will be adsorbed on the CO-desorbing oxides of OG-25, OG-400, and OG-700 after the sites, such as the C02-and H20-desorbing oxides, have been completely covered with H20.thank the Ministry of Education (Japan) for the financial support granted for this research.

Adsorption of L-DOPA and a series of other amino acids and related compounds from aqueous solutions at well-defined Pt(lll) and Pt(100) single-crystal surfaces has been studied: 3-(3,4-dihydroxyphenyl)-Lalanine (DOPA), L-tyrosine (TYR), L-cysteine (CYS), L-phenylalanine (PHE), L-alanine (ALA), dopamine (DA), catechol (CT), and (3,4-dihydroxyphenyl)acetic acid (DOPAC). Packing densities (moles adsorbed per unit area) were measured for each compound by means of quantitative Auger spectroscopy; two independent Auger spectroscopic methods were employed: one based upon measurement of elemental Auger signals from the adsorbed layer and the other upon measurement of the attenuation of the Pt Auger signal by the adsorbed layer. Packing densities of DOPA, TYR, DA, CT, and DOPAC indicate adsorption with the aromatic ring attached parallel to the surface. In contrast, CYS is adsorbed through the sulfur atom, while ALA and PHE are attached to the surface through their amino acid moieties. Vibrational spectra of the adsorbed layer formed from each of these compounds were obtained by means of electron energy-loss spectroscopy (EELS) and were compared with the infrared spectra of the parent compounds in KBr. The EELS (adsorbed layer) and IR (solid compound) spectra are similar except that the hydroxyl hydrogens of DOPA, TYR, DA, CT, and DOPAC as well as the carboxyl hydrogens of PHE and DOPAC are removed as a result of the adsorption process. EELS bands of polar groups such as O-H are not broadened to the same extent as in the IR spectra of the solid compounds, evidently due to less intermolecular bonding among such groups at the surface. LEED experiments indicate that CT forms a (3X3) adlattice at Pt(lll), while each of the other compounds forms an oriented but otherwise structurally disordered layer at Pt(lll) and Pt(100). The packing density of DOPA, CYS, and DOPAC is higher at Pt(100) than at Pt(lll) due to differences in molecular orientation. Single-crystal surface structure, adsorbate orientation, and mode of surface bonding exert a profound influence on the product distribution of electrocatalytic oxidation of these well-characterized adsorbed organic intermediates, on the basis of cyclic voltammetry and potential-step chronocoulometry experiments. This study has also revealed that evacuation does not alter the composition or electrochemical properties of the chemisorbed layer formed from solution.