The nature and properties of surface-enhanced vibrational spectra of molecules adsorbed on surfaces that can enhance the absorption and the emission of electromagnetic radiation are discussed. Examples of surface-enhanced resonant Raman scattering, surface-enhanced Raman scattering in the near-infrared and surface-enhanced infrared are given. The rough surfaces used are metal island films coated with a nanometric organic film using the Langmuir-Blodgett technique or deposited by vacuum evaporation.

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Surface enhanced vibrational spectroscopy

Electro-oxidation mechanisms of methanol and formic acid on Pt-Ru alloy surfaces

We report a combined X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and chronoamperometry (CA) study of formic acid electrooxidation on unsupported palladium nanoparticle catalysts in the particle size range from 9 to 40 nm. The CV and CA measurements show that the most active catalyst is made of the smallest (9 and 11 nm) Pd nanoparticles. Besides the high reactivity, XPS data show that such nanoparticles display the highest core-level binding energy (BE) shift and the highest valence band (VB) center downshift with respect to the Fermi level. We believe therefore that we found a correlation between formic acid oxidation current and BE and VB center shifts, which, in turn, can directly be related to the electronic structure of palladium nanoparticles of different particle sizes. Clearly, such a trend using unsupported catalysts has never been reported. According to the density functional theory of heterogeneous catalysis, and mechanistic considerations, the observed shifts are caused by...

Size effects in electronic and catalytic properties of unsupported palladium nanoparticles in electrooxidation of formic acid.

The voltammetric electrooxidation rates of formic acid, formaldehyde, and methanol in acidic electrolyte on carbon-supported platinum nanoparticle films with varying particle diameters (d) in the range of ca. 2−9 nm are examined with the objective of comparing the nanoparticle size sensitivity for these related yet distinct electrocatalytic processes. The reaction rates on the larger nanoparticles (d > 4 nm) are similar to those observed on polycrystalline Pt when normalized to the same microscopic Pt surface area. As noted previously, the rates of methanol electrooxidation decrease for Pt nanoparticle diameters below 4 nm. However, formic acid electrooxidation exhibits the opposite behavior, with rates increasing markedly for d < 4 nm, while formaldehyde electrooxidation displays little sensitivity to the Pt nanoparticle size. However, the extent of chemisorbed CO formation from all three reactants, as deduced from voltammetric and infrared spectral data, diminishes with decreasing d, the CO coverages fo...

Electrocatalytic Pathways on Carbon-Supported Platinum Nanoparticles: Comparison of Particle-Size-Dependent Rates of Methanol, Formic Acid, and Formaldehyde Electrooxidation

The spatial structure of compressed carbon monoxide adlayers on Pt(111) in aqueous acidic solution has been explored by means of in‐situ scanning tunneling microscopy (STM) along with infrared reflection–absorption spectroscopy (IRAS). Besides offering a detailed structural picture of this electrochemical interface in comparison with the well‐studied Pt(111)/CO system in ultrahigh vacuum (uhv) environments, the real‐space structural information provided by STM allows an assessment of the obfuscating influence of dynamic dipole coupling upon IRAS binding‐site assignments. In turn, the latter data provide an important crosscheck on the validity of binding‐site assignments deduced from the STM images. Emphasis is placed on the structures formed from near‐saturated CO solutions, encouraged by the electrode potential‐induced adlayer phase transition at ca. 0 V vs SCE observed previously under these conditions by IRAS. At potentials below 0 V, a hexagonal close‐packed (2×2)–3CO adlayer is observed, with a CO co...

Carbon monoxide adlayer structures on platinum (111) electrodes: A synergy between in‐situ scanning tunneling microscopy and infrared spectroscopy

Mechanisms of formic acid, methanol, and carbon monoxide electrooxidation at platinum as examined by single potential alteration infrared spectroscopy

The potential-dependent specific adsorption of acetic acid and acetate at polycrystalline platinum- and gold-aqueous interfaces has been examined by potential-difference infrared spectroscopy (PDIRS) in conjunction with quantitative surface concentration measurements using the radiotracer technique. Both the infrared and radiotracer measurements utilize a similar thin-layer solution arrangement. Extensive adsorption of acetic acid occurs at both platinum and gold, which increases at more positive potentials and reaches a maximum at the onset of anodic oxide formation. The PDIR spectra contain several features identified with solution acetic acid in the 1200-1800-cm/sup -1/ region, including v/sub C==O/ and v/sub C-O/ bands at 1710 and 1280 cm/sup -1/, respectively, arising from adsorption-induced changes in the thin-layer solution composition as well as a single band, at 1415 and 1400 cm/sup -1/ on platinum and gold, restively, due to adsorbed acetic acid. The intensity of the former bands can by employed to evaluate the extent of adsorption as a function of potential; the results are in semiquantitative agreement with the surface concentration-potential data from radiotracer measurements. In view of the infrared spectra together with the observed absence of acetate adsorption, the most likely modes of acetic acid adsorption involve hydrogen bonding between the carbonyl oxygen and inner-layermore » water molecules, of by self-association to form dimers or chain structures« less

Adsorption of acetic acid at platinum and gold electrodes: a combined infrared spectroscopic and radiotracer study

Comparaison des 2 types de spectres obtenus dans le cas de thiocyanate, de cyanure, d'azoture, de cyanate, de benzonitrile et de monoxyde de carbone adsorbes sur des electrodes d'or ou d'argent

Comparisons between surface infrared and surface-enhanced Raman spectroscopies: band frequencies, bandwidths, and selection rules for pseudohalide and related adsorbates at gold and silver electrodes

Applications au cas de l'etude de l'electrooxydation du monoxyde de carbone et de l'acide formique via Co adsorbe a l'interface platine-solution aqueuse acide

Single potential-alteration surface infrared spectroscopy: examination of absorbed species involved in irreversible electrode reactions

Coverage-dependent orientation of adsorbates as probed by potential-difference infrared spectroscopy: azide, cyanate, and thiocyanate at silver electrodes

Dennis S. Corrigan

Papers

Mechanisms of formic acid, methanol, and carbon monoxide electrooxidation at platinum as examined by single potential alteration infrared spectroscopy

Adsorption of acetic acid at platinum and gold electrodes: a combined infrared spectroscopic and radiotracer study

Comparisons between surface infrared and surface-enhanced Raman spectroscopies: band frequencies, bandwidths, and selection rules for pseudohalide and related adsorbates at gold and silver electrodes

Single potential-alteration surface infrared spectroscopy: examination of absorbed species involved in irreversible electrode reactions

Coverage-dependent orientation of adsorbates as probed by potential-difference infrared spectroscopy: azide, cyanate, and thiocyanate at silver electrodes