Application of Conventional Techniques to Study Reactions

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. 

The applications of LSV and CV to the study of chemical processes following an electron transfer reaction are so numerous that a review of the subject is clearly beyond the scope of this chapter. The examples were selected to demonstrate the application of the techniques in practical work. Although obvious, it should be emphasized that electrochemical reactions are not different from any other chemical reaction and, therefore, that the whole arsenal of methods of attack known from conventional kinetics may be used in the characterization of the process. This includes also temperature [85,120,136-138] and kinetic isotope effects [138,139]. 

We now turn to the use of Sl-SECM for the analysis of oxidizable species at electrodes, in specific for adsorbed hydrogen at through the use of oxidizing mediators. As a model application of this mode to catalysis, the decomposition of dissolved formic acid (HCOOH) on an unbiased Pt surface to produce was studied. Sl-SECM allows a simple and direct route to determine in situ the surface coverage of reaction intermediates that would otherwise remain obscured in more conventional electrochemical techniques. 

With the exception of single-crystal transmission work, most solids are too opaque to permit the conventional use of ultraviolet/visible (UV/VIS) electronic spectroscopy. As a result, such work must be performed through the use of diffuse reflection techniques [8-10]. Important work has been conducted in which UV/VIS spectroscopy has been used to study the reaction pathways of various solid state reactions. Other applications have been made in the fields of color measurement and color matching, areas which can be of considerable importance when applied to the coloring agents used in formulations. 

In addition to conventional optical spectroscopy, a number of other spectroscopic techniques have been applied to studies of expls and proplnts. Mass spectrometry applications to analysis of expl materials and combustion products, as well as characterization of reaction mechanisms are described in Refs 20, 23, 36, 38 46. A detailed discussion of mass spectrometry has previously been presented (Vol 8, M19-Lff)... 

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