Surface vibrational spectroscopic

This is a surface vibrational spectroscopic technique that involves the irradiation of the adsorbate-metal interface with a beam of low-energy (2 to 10 eV) electrons and the measurement of the energies of the backscattered electrons energy losses below 0.5 eV are due mainly to inelastic interactions with metal-surface phonons and adsorbate vibrational excitations. The extremely high sensitivity of HREELS makes possible measurements of adsor-... 

Q. Du, E. Freysz, and Y. R. Shen, Surface vibrational spectroscopic studies of hydrogen bonding and hydropohobicity. Science 264 (1994) 826. 

Du Q, Freysz E, Shen YR (1994) Surface vibrational spectroscopic studies of hydrogenbonding and hydrophobicity. Science 264(5160) 826-828... 

Vibrational spectroscopic studies of heterogeneously catalyzed reactions refer to experiments with low area metals in ultra high vacuum (UHV) as well as experiments with high area, supported metal oxides over wide ranges of pressure, temperature and composition [1]. There is clearly a need for this experimental diversity. UHV studies lead to a better understanding of the fundamental structure and chemistry of the surface-adsorbate system. Supported metals and metal oxides are utilized in a variety of reactions. Their study leads to a better understanding of the chemistry, kinetics and mechanisms in the reaction. Unfortunately, the most widely used technique for determining adsorbate molecular structure in UHV,... 

Adsorbed CO layers, bonding and Interactions, 559-61 Adsorbed molecules, vibrational analysis, 392-V03 Adsorbed species and processes on surfaces, IR spectroscopic characterizations, VOV-19 Adsorption... 

In practice, surface modifications are restricted to sensors of the ATR- or FEWS-type. For other transducer layouts, the sample - radiation interaction is less localised, making a modification difficult to impossible. Depending on the analytes and the environment of the sensor, two basic surface modification strategies can be used to enhance the function of vibrational spectroscopic optical chemical sensors. The functional layers can either be... 

The Scanning Tunneling Microscope has demonstrated unique capabilities for the examination of electrode topography, the vibrational spectroscopic imaging of surface adsorbed species, and the high resolution electrochemical modification of conductive surfaces. Here we discuss recent progress in electrochemical STM. Included are a comparison of STM with other ex situ and in situ surface analytic techniques, a discussion of relevant STM design considerations, and a semi-quantitative examination of faradaic current contributions for STM at solution-covered surfaces. Applications of STM to the ex situ and in situ study of electrode surfaces are presented. 

A major emerging area of research activity in interfacial electrochemistry concerns the development of in-situ surface spectroscopic methods, especially those applicable in conventional electrochemical circumstances. One central objective is to obtain detailed molecular structural information for species within the double layer to complement the inherently macroscopic information that is extracted from conventional electrochemical techniques. Vibrational spectroscopic methods are particularly valuable for this purpose in view of their sensitivity to the nature of intermolecular interactions and surface bonding as well as to molecular structure. Two such techniques have been demonstrated to be useful in electrochemical systems surface-enhanced Raman spectroscopy... 

In addition to the indirect experimental evidence coming from work function measurements, information about water orientation at metal surfaces is beginning to emerge from recent applications of a number of in situ vibrational spectroscopic techniques. Infrared reflection-absorption spectroscopy, surface-enhanced Raman scattering, and second harmonic generation have been used to investigate the structure of water at different metal surfaces, but the pictures emerging from all these studies are not always consistent, partially because of surface modification and chemical adsorption, which complicate the analysis. 

Teplyakov, A. V., Kong, M. J. and Bent, S. F. Vibrational spectroscopic studies of Diels-Alder reactions with the Si(100)—2 x 1 surface as a dienophile. Journal of the American Chemical Society 119, 11100 (1997). 

Relatively few vibrational spectroscopic investigations have been reported for acyclic alkanes, whether adsorbed on single-crystal or on finely divided metal surfaces. The spectra of the cyclic alkanes are more conveniently discussed later (Section V.A) because of their relationships to the spectra of aromatic species into which they are readily converted by metal catalysts. 

Comparisons with the vibrational spectroscopic studies of the adsorption and dehydrogenation of ethene on single-crystal Pt surfaces (Section X.B.l) show that the di-cr-C2H4 to ethylidyne conversion occurs on (111) facets of the Pt crystallites of the catalysts. It is considered that the di-cr -C2H4 species occur on metal sites on which this conversion is not allowed, perhaps on (100), (110), or (210) facets. It is not clear whether the labile it-C2H4 species is formed on amorphous areas of the clean Pt particles or whether it occurs on sites which are affected by proximity of the metal oxide support (408) we favor the former possibility. 

VEEL or RAIR spectroscopy to provide insight into temperature-dependent surface reactions. The TPD technique also provides information about the overall C/H composition of the hydrocarbon layers at different temperatures. Whereas we have made reference to, and taken into account, experimental results obtained from the use of such nonvibrational techniques in many cases, particularly when considering spectral interpretaions, it has not been feasible for us to systematically cover such papers that do not also include vibrational spectroscopic work. 

The present-day literature contains many more spectra obtained from singlecrystal metal surfaces by VEELS than by RAIRS. However, the much higher resolution available from the more recently developed RAIRS technique and its capability of operating in the presence of a gas phase suggest that it will contribute increasingly important information in the hydrocarbon adsorption field. The three spectroscopic techniques discussed above are much the most important ones in this area, with transmission infrared spectroscopy as the predominantly useful one for work with finely divided samples. A few other vibrational spectroscopic techniques (25) have provided information on adsorbed hydrocarbons, but are at present of more limited or specialized applications. Their principal characteristics are more briefly summarized below. 

Johnson et al. (132) have also discussed the validity or otherwise of such analogies. Spectra from the same type of surface species that give similar vibrational spectroscopic patterns can show readily measurable frequency variations that may be much more significant in reactivity terms. However, it seems clear that in many cases the overall spectral patterns of cluster-compound ligands do provide useful and reliable fingerprints for identifying the structures of surface species. 

In this article (Part I) we have comprehensively reviewed the structural implications of the vibrational spectroscopic results from the adsorption of ethene and the higher alkenes on different metal surfaces. Alkenes were chosen for first review because the spectra of their adsorbed species have been investigated in most detail. It was to be expected that principles elucidated during their analysis would be applicable elsewhere. The emphasis has been on an exploration of the structures of the temperature-dependent chemisorbed species on different metal surfaces. Particular attention has been directed to the spectra obtained on finely divided (oxide-supported) metal catalysts as these have not been the subject of review for a long time. An opportunity has, however, also been taken to update an earlier review of the single-crystal results from adsorbed hydrocarbons by one of us (N.S.) (7 7). Similar reviews of the fewer spectra from other families of adsorbed hydrocarbons, i.e., the alkynes, the alkanes (acyclic and cyclic), and aromatic hydrocarbons, will be presented in Part II. 

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