Brief

In this Dictionary 1 have aimed to provide an explanation of the terms used in the various branches of chemistry, together with brief accounts of important substances and chemical operations. The Dictionary is intended for use in schools, colleges and universities from the first study of chemistry up to about second year at university or college. We have necessarily had to be selective rather than comprehensive but most chemicals met with at this level should be included. 

Based on a series of briefs published in the Economist in 1984, this important new book makes the key issues of contemporary economic thinking accessible to the general reader. 

We will begin by a brief review of the concept of the X-ray fluorescence analytical method widely used in the petroleum industry for studying the whole range of products and for analyzing catalysts as well. 

A study is at present being carried out to check and validate the feasability of acoustic emission monitoring of the pneumatic testing of tanks. This study is being carried out in the context of the CIAPES program. This article gives only a brief summary of the results obtained on various materials, and different types of vessels, under different operating conditions. 

Experience of AUGUR4.2 applications during 1996 ISI of primary circulation piping weldments at RBMK NPP Units has been presented before [1,2], and only in brief is drawn hereafter. 

A brief description of probe types and their characteristics would be appropriate Absolute Probes... 

The following table 1 gives brief presentation of physical methods used for this or that diagnostic procedure. 

Table 2 Brief Content of NDTnet in 1996 -1997 (Source NDTnet 97 CD-ROM)...

To resume the brief historical sketch, the subject of monolayers developed rapidly during the interwar years, with the names of Langmuir, Adam, Harkins, and Rideal perhaps the most prominent the subject became one of precise and... 

In recent years, advances in experimental capabilities have fueled a great deal of activity in the study of the electrified solid-liquid interface. This has been the subject of a recent workshop and review article [145] discussing structural characterization, interfacial dynamics and electrode materials. The field of surface chemistry has also received significant attention due to many surface-sensitive means to interrogate the molecular processes occurring at the electrode surface. Reviews by Hubbard [146, 147] and others [148] detail the progress. In this and the following section, we present only a brief summary of selected aspects of this field. 

In this section we consider electromagnetic dispersion forces between macroscopic objects. There are two approaches to this problem in the first, microscopic model, one assumes pairwise additivity of the dispersion attraction between molecules from Eq. VI-15. This is best for surfaces that are near one another. The macroscopic approach considers the objects as continuous media having a dielectric response to electromagnetic radiation that can be measured through spectroscopic evaluation of the material. In this analysis, the retardation of the electromagnetic response from surfaces that are not in close proximity can be addressed. A more detailed derivation of these expressions is given in references such as the treatise by Russel et al. [3] here we limit ourselves to a brief physical description of the phenomenon. 

The resistance to nucleation is associated with the surface energy of forming small clusters. Once beyond a critical size, the growth proceeds with the considerable driving force due to the supersaturation or subcooling. It is the definition of this critical nucleus size that has consumed much theoretical and experimental research. We present a brief description of the classic nucleation theory along with some examples of crystal nucleation and growth studies. 

Adsorption at a charged surface where both electrostatic and speciflc chemical forces are involved has been discussed to some extent in connection with various other topics. These examples are drawn together here for a brief review along with some more speciflc additional material. The Stem equation, Eq. V-19, may be put in a form more analogous to the Langmuir equation, Eq. XI-4 ... 

Brief mention should be made of the important topic of aerosols, more or less stable suspensions of liquid or solid particles in a gas. The manufacture... 

Traditionally one categorizes matter by phases such as gases, liquids and solids. Chemistry is usually concerned with matter m the gas and liquid phases, whereas physics is concerned with the solid phase. However, this distinction is not well defined often chemists are concerned with the solid state and reactions between solid-state phases, and physicists often study atoms and molecular systems in the gas phase. The tenn condensed phases usually encompasses both the liquid state and the solid state, but not the gas state. In this section, the emphasis will be placed on the solid state with a brief discussion of liquids. 

This section begins with a brief description of the basic light-molecule interaction. As already indicated, coherent light pulses excite coherent superpositions of molecular eigenstates, known as wavepackets , and we will give a description of their motion, their coherence properties, and their interplay with the light. Then we will turn to linear and nonlinear spectroscopy, and, finally, to a brief account of coherent control of molecular motion. 

In the presence of some fomi of relaxation the equations of motion must be supplemented by a temi involving a relaxation superoperator—superoperator because it maps one operator into another operator. The literature on the correct fomi of such a superoperator is large, contradictory and incomplete. In brief, the extant theories can be divided into two kinds, those without memory relaxation (Markovian) Tp and those with memory... 

Below are brief descriptions of some of the particle-surface interactions important in surface science. The descriptions are intended to provide a basic understanding of how surfaces are probed, as most of the infonuation that we have about surfaces was obtained tluough the use of techniques that are based on such interactions. The section is divided into some general categories, and the important physics of the interactions used for analysis are emphasized. All of these teclmiques are described in greater detail in subsequent sections of the encyclopaedia. Also, note that there are many more teclmiques than just those discussed here. These particular teclmiques were chosen not to be comprehensive, but instead to illustrate the kind of infonuation that can be obtained from surfaces and interfaces. 

Finally, a brief sunnnary of the known behaviour of activity coefficients Binary non-electrolyte mixtures ... 

Any detailed discussion of statistical mechanics would be hiappropriate for this section, especially since other sections (A2.2 and A2.3) treat this in detail. However, a few aspects that relate to classical themiodynaniics deserve brief mention. 

In this brief review of dynamics in condensed phases, we have considered dense systems in various situations. First, we considered systems in equilibrium and gave an overview of how the space-time correlations, arising from the themial fluctuations of slowly varying physical variables like density, can be computed and experimentally probed. We also considered capillary waves in an inliomogeneous system with a planar interface for two cases an equilibrium system and a NESS system under a small temperature gradient. 

The foundations of the modem tireory of elementary gas-phase reactions lie in the time-dependent molecular quantum dynamics and molecular scattering theory, which provides the link between time-dependent quantum dynamics and chemical kinetics (see also chapter A3.11). A brief outline of the steps hr the development is as follows [27],... 

In the sections below a brief overview of static solvent influences is given in A3.6.2, while in A3.6.3 the focus is on the effect of transport phenomena on reaction rates, i.e. diflfiision control and the influence of friction on intramolecular motion. In A3.6.4 some special topics are addressed that involve the superposition of static and transport contributions as well as some aspects of dynamic solvent effects that seem relevant to understanding the solvent influence on reaction rate coefficients observed in homologous solvent series and compressed solution. More comprehensive accounts of dynamics of condensed-phase reactions can be found in chapter A3.8. chapter A3.13. chapter B3.3. chapter C3.1. chapter C3.2 and chapter C3.5. 

The treatment of equilibrium solvation effects in condensed-phase kmetics on the basis of TST has a long history and the literature on this topic is extensive. As the basic ideas can be found m most physical chemistry textbooks and excellent reviews and monographs on more advanced aspects are available (see, for example, the recent review article by Tnihlar et al [6] and references therein), the following presentation will be brief and far from providing a complete picture. 

The above discussion represents a necessarily brief simnnary of the aspects of chemical reaction dynamics. The theoretical focus of tliis field is concerned with the development of accurate potential energy surfaces and the calculation of scattering dynamics on these surfaces. Experimentally, much effort has been devoted to developing complementary asymptotic techniques for product characterization and frequency- and time-resolved teclmiques to study transition-state spectroscopy and dynamics. It is instructive to see what can be accomplished with all of these capabilities. Of all the benclunark reactions mentioned in section A3.7.2. the reaction F + H2 —> HE + H represents the best example of how theory and experiment can converge to yield a fairly complete picture of the dynamics of a chemical reaction. Thus, the remainder of this chapter focuses on this reaction as a case study in reaction dynamics. 

This chapter will explore surface reactions at the atomic level. A brief discussion of corrosion reactions is followed by a more detailed look at growth and etchmg reactions. Finally, catalytic reactions will be considered, with a strong emphasis on the surface science approach to catalysis. 

In this chapter we shall first outline the basic concepts of the various mechanisms for energy redistribution, followed by a very brief overview of collisional intennoleciilar energy transfer in chemical reaction systems. The main part of this chapter deals with true intramolecular energy transfer in polyatomic molecules, which is a topic of particular current importance. Stress is placed on basic ideas and concepts. It is not the aim of this chapter to review in detail the vast literature on this topic we refer to some of the key reviews and books [U, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, and 32] and the literature cited therein. These cover a variety of aspects of tire topic and fiirther, more detailed references will be given tliroiighoiit this review. We should mention here the energy transfer processes, which are of fiindamental importance but are beyond the scope of this review, such as electronic energy transfer by mechanisms of the Forster type [33, 34] and related processes. 

Section BT1.2 provides a brief summary of experimental methods and instmmentation, including definitions of some of the standard measured spectroscopic quantities. Section BT1.3 reviews some of the theory of spectroscopic transitions, especially the relationships between transition moments calculated from wavefiinctions and integrated absorption intensities or radiative rate constants. Because units can be so confusing, numerical factors with their units are included in some of the equations to make them easier to use. Vibrational effects, die Franck-Condon principle and selection mles are also discussed briefly. In the final section, BT1.4. a few applications are mentioned to particular aspects of electronic spectroscopy. 

Raman spectroscopy is pervasive and ever changing in modem physics and chemistry. In this section of the chapter, sources of up-to-date infonnation are given followed by brief discussions of a number of currently employed Raman based teclmiques. It is unpractical to discuss every possible technique and impossible to predict the many future novel uses of Raman scattering that are sure to come, but it is hoped that this section will provide a finu launching point into the modem uses of Raman spectroscopy for present and fiiture readers. 

The third important source for infonnation on modem Raman spectroscopy are the books cataloguing the proceedings of the International Conference on Raman Spectroscopy (ICORS) [37]. ICORS is held every two years at various international locations and feahires hundreds of contributions from leading research groups covering all areas of Raman spectroscopy. Although the published presentations are quite limited in lengdi, they each contain references to the more substantial works and collectively provide an excellent overview of current trends m Raman spectroscopy. A snapshot or brief sununary of the 1998 conference appears at the end of this chapter. 

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