Vibrational spectroscopy features

The high stability of fluoride complexes maintains the configuration and vibration parameters of different compounds in various media. This special feature enables clear distinguishing of different complex ion types using vibration spectroscopy in solid, liquid and molten media. 

One of the most common uses of vibrational spectroscopy is as a molecular fingerprinting tool whereby spectral features are assigned to the presence of particular fragments in molecules. These assignments are, however, only... 

In addition to the surface/interface selectivity, IR-Visible SFG spectroscopy provides a number of attractive features since it is a coherent process (i) Detection efficiency is very high because the angle of emission of SFG light is strictly determined by the momentum conservation of the two incident beams, together with the fact that SFG can be detected by a photomultiplier (PMT) or CCD, which are the most efficient light detectors, because the SFG beam is in the visible region, (ii) The polarization feature that NLO intrinsically provides enables us to obtain information about a conformational and lateral order of adsorbed molecules on a flat surface, which cannot be obtained by traditional vibrational spectroscopy [29-32]. (iii) A pump and SFG probe measurement can be used for an ultra-fast dynamics study with a time-resolution determined by the incident laser pulses [33-37]. (iv) As a photon-in/photon-out method, SFG is applicable to essentially any system as long as one side of the interface is optically transparent. 

The use of vibrational spectroscopy for the qualitative analysis of absorbed surface species is first considered, and a Table is then included which summarises a number of the key features of the various quantitative techniques. We then proceed to summarize these in groups depending not upon the probe used (as in the preceding chapters), but in terms of the signal emitted by the specimen which is used in each identification process. 

The adsorption of CO on Pt is perhaps the most throughly studied system using vibrational spectroscopy. Studies have been made using both supported catalysts (2-5) and single crystals (5-10). Sample environments have included gas phase, vacuum, and aqueous solution (11-13). The similarities between many of these results have led to a remarkably unified understanding of CO adsorption phenomena in all three environments. Features which are relevant to further studies of the metal/electrolyte interface are summarized briefly ... 

With the stability of this intermediate established, its spectral features in photoemission and high resolution electron energy loss (vibrational) spectroscopy (EELS) could be determined. Indeed, with ultraviolet photoelectron spectra (UPS) it was shown that methanol reacted with the preadsorbed oxygen to... 

The period under review has seen a small, but apparently real, decrease in the annual number of publications in the field of the vibrational spectroscopy of transition metal carbonyls. Perhaps more important, and not unrelated, has been the change in perspective of the subject over the last few years. Although it continues to be widely used, the emphasis has moved from the simple method of v(CO) vibrational analysis first proposed by Cotton and Kraihanzel2 which itself is derived from an earlier model4 to more accurate analyses. One of the attractions of the Cotton-Kraihanzel model is its economy of parameters, making it appropriate if under-determination is to be avoided. Two developments have changed this situation. Firstly, the widespread availability of Raman facilities has made observable frequencies which previously were either only indirectly or uncertainly available. Not unfrequently, however, these additional Raman data have been obtained from studies on crystalline samples, a procedure which, in view of the additional spectral features which can occur with crystalline solids (vide infra), must be regarded as questionable. The second source of new information has been studies on isotopically-labelled species. 

Vibrational spectroscopy, in the form of mid-IR, NIR and Raman spectroscopy has been featured extensively in industrial analyses, both quality control (QC), process monitoring applications and held-portable applications [1-6]. The latter has been aided by the need for advanced instrumentation for homeland security and related HazMat applications. Next to chromatography, it is the most widely purchased classihcation of instrumentation for these measurements and analyses. Spectroscopic methods in general are favored because they are relatively straightforward to apply and to implement, are rapid in terms of providing results, and are often more economical in terms of service, support and maintenance. Furthermore, a single spectrometer or spectral analyzer, in a near-line application, may serve many functions, whereas chromatographs (gas and liquid) tend to be dedicated to only a few methods at best. 

It should be noted that for many spectroscopies, the integrated peak area rather than peak height remains proportional to the moles of solute present, even over large regions of composition space. This quantitative feature of integrated areas has a precise analytical form in vibrational spectroscopy [72, 73]. 

The application of spectroscopic techniques familiar in organometallic chemistry to the unique features of carbidocarbonyl clusters has become more evident since the previous review of this field (1). Vibrational spectroscopy and 13C NMR have yielded useful data relevant to the geometric and... 

The cross-section in Eq. (1 illustrates another distinguishing feature of inelastic neutron scattering for vibrational spectroscopy, i.e., the absence of dipole and polarizability selection rules. In contrast, it is believed that in optical and inelastic electron surface spectroscopies that a vibrating molecule must possess a net component of a static or induced dipole moment perpendicular to a metal surface in order for the vibrational transition to be observed ( 7,8). This is because dipole moment changes of the vibrating molecule parallel to the surface are canceled by an equal image moment induced in the metal. 

Although the question of orientation order does not arise, these results for argon monolayers illustrate several features of neutron vibrational spectroscopy. Well-defined excitations can be observed at somewhat lower energy transfers than accessible with optical and electron energy-loss spectroscopies. Typical energy resolution in the scans of Fig. 2 is 0.3 meV (2.4 cm"1). The capability of obtaining inelastic spectra at constant non-zero Q is also not present in these other spectroscopies. However, scattered intensities are relatively low. Counting times in Fig. 2 were -30 minutes per point. 

Various forms of molecular carbon, from ions to radicals, have been detected in the diffuse interstellar medium (ISM) using electronic, rotational, and vibrational spectroscopies (Henning and Salama 1998 Snow and Witt 1995). Discrete absorption and emission bands seen toward diffuse interstellar clouds indicate the presence of numerous two-atom molecules such as CO, CN and C2. In addition to these interstellar features, a large family of spectral bands observed from the far-UV to the far-IR still defies explanation. Currently, it is the general consensus that many of the unidentified spectral features are formed by a complex, carbonaceous species that show rich chemistry in interstellar dust clouds (Ehrenfreund... 

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