Vibrations surfaces , spectroscopic

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... 

The only points on the potential surface for which experimental data are available are the minima, corresponding to stable molecules whose properties can be studied. The geometry of a molecule corresponds to the coordinates of the corresponding point and its heat of formation to the height of the point in the potential surface. The frequenciesof molecular vibrations, determined spectroscopically, allow one to also estimate the curvature of the potential surface at the minimum. It is easily seen that all these quantities must be reproduced by our theoretical treatment if it is to be applied to calculations of reaction paths. 

The use of optical methods which probe interface electronic and vibrational resonances offers significant advantages over conventional surface spectroscopic methods in which, e.g. beams of charged particles are used as a probe, or charged particles emitted from the surface/interface after photon absorption are detected. Recently, three-wave mixing techniques such as second-harmonic generation (SHG) have become important tools to study reaction processes at interfaces. SHG is potentially surface-sensitive at nondestructive power densities, and its application is not restricted to ultrahigh vacuum (UHV) conditions.However, SHG suffers from a serious drawback, namely from its lack of molecular selectivity. As a consequence, SHG cannot be used for the identification of unknown surface-species. 

Over the next few years, both the mid-infrared and the far-infrared spectra for Ar-HF and Ar-HCl were extended to numerous other bands and to other isotopic species (most importantly those containing deuterium). In 1992, Hutson [18, 39] combined all the available spectroscopic data to produce definitive potential energy surfaces that included both the angle dependence and the dependence on the HF/HCl monomer vibrational quantum number v... 

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... 

Each spectroscopic technique (electronic, vibra-tional/rotational, resonance, etc.) has strengths and weaknesses, which determine its utility for studying polymer additives, either as pure materials or in polymers. The applicability depends on a variety of factors the identity of the particular additive(s) (known/unknown) the amount of sample available the analysis time desired the identity of the polymer matrix and the need for quantitation. The most relevant spectroscopic methods commonly used for studying polymers (excluding surfaces) are IR, Raman (vibrational), NMR, ESR (spin resonance), UV/VIS, fluorescence (electronic) and x-ray or electron scattering. 

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