Physical properties, laser spectroscopy

The crystalline mineral silicates have been well characterized and their diversity of stmcture thoroughly presented (2). The stmctures of siHcate glasses and solutions can be investigated through potentiometric and dye adsorption studies, chemical derivatization and gas chromatography, and laser Raman, infrared (ftir), and Si Fourier transform nuclear magnetic resonance ( Si ft-nmr) spectroscopy. References 3—6 contain reviews of the general chemical and physical properties of siHcate materials. 

Structural studies in fused salts by means of careful and thorough high-temperature measurements of electrical conductivity, density, viscosity, and laser- Raman spectroscopy have been reviewed. Four problem areas are discussed (1) melting mechanisms of ionic compounds with large polyatomic cations, (2) salts as ultra-concentrated electrolyte solutions, (3) structural aspects and Raman spectroscopy, and (4) electrolysis of molten carbonates. The results in these areas are summarized and significant contributions to new experimental techniques for molten-salt studies are discussed.275 The physical properties and structure of molten salts have also been reviewed in terms of operational (hole, free volume, partly disordered crystal) and a priori (intermolecular potential) models.276 Electrochemistry... 

Laser-source confocal Raman spectroscopy was used to analyze solid dispersions to evaluate the physical properties and determine the distribution of ibuprofen in extrudates of polyvinylpyrrolidone (PVP). As is shown in Figure 14, a shift in the Raman spectra occurs when the crystalline form of ibuprofen is compared to a solution or a PVP extrudate containing ibuprofen. For comparison purposes, ibuprofen was completely dissolved in dimeric... 

We will discuss the application of multistep laser excitation and ionization to determine the physical properties mentioned above in the lanthanides and actinides with emphasis on the determination of accurate ionization potentials. The discussion will point out how the laser techniques can circumvent many of the experimental obstacles that make these measurements difficult or impossible by conventional spectroscopy. The experimental apparatus and techniques described can be employed to measure all the properties and they are typical of the apparatus and techniques employed generally in multistep laser excitation and ionization. We do not claim completeness for literature cited, especially for laser techniques not involving photoionization detection. 

Infrared spectroscopy has been a widely used tool for the study of organic solvent systems for many years and the techniques involved can be learned from many good monographs. " Raman spectroscopy has also been employed to provide significant information about the constitution and physical properties of these systems. Until the recent advent of the laser, however, Raman facilities were only available in a few laboratories and a general lack of familiarity with the principles and the potential of this approach existed. In the immediate future we can expect many new results from this form of spectroscopy and a brief discussion of the principles and techniques is in order. 

A classification scheme for laser-microwave spectroscopy based on well-defined three-step processes is displayed in Figure 5. It illustrates the great variety of possible experimental methods. The steps can be carried out in many different ways depending, for example, on the physical properties of the species under study. To be more specific, details of the three steps are as follows ... 

Chemical analysis of polymers typically deals with monomers or functional groups rather than constituent atoms. Thermal infrared and laser optical Raman spectrometry are the typical tools (36) (see Test Methods Vibrational Spectroscopy), but frequently, specific specimen size or form is required. For physical properties, mechanical and sonic/ultrasonic NDT methods are available (see above). Molecular mass distribution and related properties of polymers, or fiber or particle volume fraction and distribution for PMC, are usually determined destructively (see Test Methods). 

The first volume contains the basic physical foundations of laser spectroscopy and the most important experimental equipment in a spectroscopic laboratory. It begins with a discussion of the fundamental definitions and concepts of classical spectroscopy, such as thermal radiation, induced and spontaneous emission, radiation power, intensity and polarization, transition probabilities, and the interaction of weak and strong electromagnetic (EM) fields with atoms. Since the coherence properties of lasers are important for several spectroscopic techniques, the basic definitions of coherent radiation fields are outlined and the description of coherently excited atomic levels is briefly discussed. 

In concluding this section, we emphasize that we have selected a few of the techniques and spectroscopic applications out of the multitude of methods which now comprise the experimental field of laser spectroscopy. The choice of laser based methods for description is biased by their general applicabihty to the subject of interest in this series of handbook volumes which is the elucidation of the physical and chemical properties of lanthanide systems. 

Development of this kind of knowledge about excited states is likely to be slow, however moreover, the equipment is highly specialized and its use is more likely to be in the hands of spectroscopically oriented chemical physicists than in those of coordination chemists. For this reason, however, we can expect increasing collaboration between laboratories having different and complementary capabilities. There is another point to be made about laser spectroscopy. It is now possible to do state-to-state photochemistry on a long femtosecond time scale, that is, to pinpoint the vibrational level of the excited state and that of the immediately produced product state. At this point I believe that we have left the realm of chemistry and entered that of physics and spectroscopy for their own sake. What seems important to me, as a physical chemist, is to know the structure and electronic properties of thexi states rather than those of spectroscopic states. Notice that there are two distinct usages of the word "state" that of a thermodynamic state or ensemble, i.e. of a thexi state, and that of a particular molecular wave-mechanical or spectroscopic state. 

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