Spectroscopy laser techniques

Hepburn J W 1995 Generation of coherent vacuum ultraviolet radiation applications to high-resolution photoionization and photoelectron spectroscopy Laser Techniques in Chemistry vol 23, ed A B Myers and T R Rizzo (New York Wley) pp 149-83... 

The first Raman and infrared studies on orthorhombic sulfur date back to the 1930s. The older literature has been reviewed before [78, 92-94]. Only after the normal coordinate treatment of the Sg molecule by Scott et al. [78] was it possible to improve the earlier assignments, especially of the lattice vibrations and crystal components of the intramolecular vibrations. In addition, two technical achievements stimulated the efforts in vibrational spectroscopy since late 1960s the invention of the laser as an intense monochromatic light source for Raman spectroscopy and the development of Fourier transform interferometry in infrared spectroscopy. Both techniques allowed to record vibrational spectra of higher resolution and to detect bands of lower intensity. 

The vibrational spectrum of a metal complex is one of the most convenient and unambigious methods of characterization. However, it has not been possible to study the interactions of metal ions and biological polymers in this way since the number of vibrational bands from the polymer obscure the metal spectrum. The use of laser techniques for Raman spectroscopy now make it very likely that the Raman spectra of metals in the presence of large amounts of biological material will be measured (34). The intensity of Raman lines from metal-ligand vibrations can be... 

The historical development and elementary operating principles of lasers are briefly summarized. An overview of the characteristics and capabilities of various lasers is provided. Selected applications of lasers to spectroscopic and dynamical problems in chemistry, as well as the role of lasers as effectors of chemical reactivity, are discussed. Studies from these laboratories concerning time-resolved resonance Raman spectroscopy of electronically excited states of metal polypyridine complexes are presented, exemplifying applications of modern laser techniques to problems in inorganic chemistry. 

The following case study contains examples of several topics discussed in previous sections, including some aspects of laser technology, laser spectroscopy and laser chemistry. A variety of lasers and laser techniques are applied in a straightforward manner to the problem of ascertaining structural and dynamical information on an excited electronic state of wide chemical interest. This information is obtained rather simply, illustrating the potential of laser techniques in the resolution of problems in solution chemistry. 

Photon correlation spectroscopy A technique for measuring the size of submicrometer particles by analyzing their size-dependent scattering of laser light. 

In this review, we describe a laser trapping-spectroscopy-electrochemistry technique as a novel methodology for studying single microdroplets in solution and, demonstrate recent progress in the research on electron transfer and mass transfer across a microdroplet/solution interface in special reference to a droplet size dependence of the process. 

The laser trapping-spectroscopy-electrochemistry technique is unique in that simultaneous three-dimensional manipulation and spectroscopic/elec-trochemical measurements can be conducted for individual microdroplets in solution. Although the technique is highly useful for studying single microdroplets, its applicability and limitations have not been well documented until now. Therefore, before discussing detailed chemistry of single droplets in solution, we describe briefly the characteristics of the technique. 

In Sections III and IV, we described droplet size dependencies of the ET and MT rates across microdroplet/water interfaces. Such experiments on single droplets are possible by the laser trapping spectroscopy-electrochemistry technique alone. Besides these experiments, the technique is also highly useful in controlling a reaction efficiency in microdroplets [99,100]. In this section, we describe electrochemically induced dye formation reactions across microdroplet/water interface and demonstrate control of the dye formation reaction yield in micrometer dimension. The effects of microenvironments and additives (surfactant or stabilizer) on dye formation reactions are also described. 

Direct determination of the rate of the C- or Y-Dye formation reaction in the individual microdroplets has been made possible by potential application of the laser trapping-spectroscopy-electrochemistry technique. Furthermore, the dye formation reaction efficiency in each droplet could be controlled arbitrarily by the distance between the droplet and the electrode. Under the present experimental conditions (i.e., pH 10 and [SO] ] =20mM), the diffusion length of QDI within its lifetime is only several micrometers, so the distance dependence of the reaction is unique in the micrometer dimension. The present approach will therefore lead to a new methodology to control chemical reaction in micrometer-size volumes. 

The laser trapping-spectroscopy-electrochemistry technique, capable of single microdroplet measurements, is shown to be indispensable in elucida-... 

Some very important surface properties of solids can be properly characterized only by certain wet chemical techniques, some of which are currently under rapid improvement. Studies of adsorption from solution allow determination of the surface density of adsorbing sites, and the characterization of the surface forces involved (the energy of dispersion forces, the strength of acidic or basic sites and the surface density of coul-ombic charge). Adsorption studies can now be extended with some newer spectroscopic tools (Fourier-transform infra-red spectroscopy, laser Raman spectroscopy, and solid NMR spectroscopy), as well as convenient modern versions of older techniques (Doppler electrophoresis, flow microcalorimetry, and automated ellipsometry). 

Although it might appear that this technique is in some respect surpassed by the more powerful and versatile photon correlation spectroscopy (laser beat spectroscopy) which will be discussed in a later paragraph, it can still serve as a convenient method to study the absolute scattered intensity of small colloidal particles. 

The conventional flash photolysis setup to study photochemical reactions was drastically improved with the introduction of the pulsed laser in 1970 [17], Soon, nanosecond time resolution was achieved [13], However, the possibility to study processes faster than diffusion, happening in less than 10 10 s, was only attainable with picosecond spectroscopy. This technique has been applied since the 1980s as a routine method. There are reviews covering the special aspects of interest of their authors on this topic by Rentzepis [14a], Mataga [14b], Scaiano [18], and Peters [14c],... 

Among other new methods, tunable laser absorption spectroscopy using infrared diode lasers offers prospects for improved accuracy and specificity in concentration measurements, when a line-of-sight technique is appropriate. The present paper discusses diode laser techniques as applied to a flat flame burner and to a room temperature absorption cell. The cell experiments are used to determine the absorption band strength which is needed to properly interpret high temperature experiments. Preliminary results are reported for CO concentration measurements in a flame, the fundamental band strength of CO at STP, collision halfwidths of CO under flame conditions, and the temperature dependence of CO and NO collision halfwidths in combustion gases. 

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