Visible Raman spectroscopy analysis

There are currently three different Raman spectrometer systems that are employed for catalyst characterization conventional or visible Raman (400-700 nm) [9], FT-Raman (750-1100 nm) [147], and UV-Raman (200-350 nm) [148]. Each of these Raman spectrometer systems possesses advantages and disadvantages for the different types of catalytic materials, as summarized in Table 6. Visible Raman spectroscopy is generally excellent for ambient analysis of most catalyst types because its relatively mild energy, especially when coupled with sample spinning, generally does not perturb the natural state of the sample (i.e., degree of hydration). However, visible Raman is susceptible to fluorescence problems that can dominate the spectrum. Fluorescence is very common with... 

Materials characterization techniques, ie, atomic and molecular identification and analysis, ate discussed ia articles the tides of which, for the most part, are descriptive of the analytical method. For example, both iaftared (it) and near iaftared analysis (nira) are described ia Infrared and raman SPECTROSCOPY. Nucleai magaetic resoaance (nmr) and electron spia resonance (esr) are discussed ia Magnetic spin resonance. Ultraviolet (uv) and visible (vis), absorption and emission, as well as Raman spectroscopy, circular dichroism (cd), etc are discussed ia Spectroscopy (see also Chemiluminescence Electho-analytical techniques It unoassay Mass specthot thy Microscopy Microwave technology Plasma technology and X-ray technology). 

Raman spectroscopy detects the scattering of light, not its absorption. Superposed on the frequency of the scattered light are the frequencies of the molecular vibrations. The detection occurs in the IR spectral region while the excitation happens in the visible region. Since laser light sources have become well developed, Raman spectroscopy has become an important tool for the analysis of biomolecules. 

Raman spectroscopy, while typically used as a micro-analytical tool, can be conducted remotely. Performance of remote Raman analysis have been recently explored and reahzed for experiments on the surface of Mars (Sharma et al. 2001 Sharma et al. 2003). Raman spectroscopy is a powerful technique for mineralogical analysis, where the sharpness of spectral features of minerals allows for much less ambiguous detection, especially in the presence of mixtures. Visible, near-infrared, thermal, reflectance and in many cases emission spectroscopy of minerals all suffer from broad overlapping spectral features, which complicates interpretation of their spectra. On the other hand, Raman spectra of minerals exhibit sharp and largely non-overlapping features that are much more easily identified and assigned to various mineral species. 

PHOTOMETRIC ANALYSIS. Chemical analysis by means of absorption or emission of radiation, primarily in the near UV, visible, and infrared portions of the electromagnetic spectrum. It includes such techniques as spectrophotometry, spectrochemical analysis, Raman spectroscopy, colorimetry, and fluorescence measurements. 

Raman spectroscopy has some particular advantages for biofluid analysis as well. The sharpness of fundamental vibrational peaks enables dense packing of information into a spectral interval, much more so than for the broader peaks typical of fluorescence or visible/NIR absorption. These extra degrees of spectral freedom are important when it comes to measuring the concentration of minor contributors above the various noise sources. 

Raman spectroscopy can be used to detect normal modes of target molecules and also to monitor spectra of Raman labels that are used for one of the spectroscopic bar-codes. Raman bands in the vibrational Raman spectmm have intrinsically narrow bandwidths of ca. 10 cm, which, for example, correspond to less than 0.5 nm width in the visible region below 800 nm. The fluorescence of dye molecules has a broad bandwidth of 100 nm more or less. Hence, spectral overlap between fluorescence bands is inevitable and limits their use for multiplexed analysis. Quantum dots (QDs) have narrower bandwidth than dye-based fluorescence but stUl have broad bands that are several tens of nanometers. Light scattering of noble metal nanoparticles caused by surface plasmon resonance is also... 

The most conventional excitation source for Raman spectroscopy, a 514-nm Ar-ion laser, is known to cause a strong fluorescence during the analysis of ND samples. Compared to visible Raman, UV-Raman analysis offers a stronger diamond signal due to the resonance enhancement effect [85]. It is therefore preferred to use UV (244 and 325 nm) excitations for the analysis of ND powders. 

Elemental analysis UV/Visible spectroscopy Infrared spectroscopy Raman spectroscopy X-ray diffraction... 

In the visible Raman spectra the cross section of the sp phase is much higher (50-250 times for 514.5 nm) than that of the sp phase. Hence UV Raman spectroscopy (Renishaw 2000 system) with a He- Cd laser (325 nm wavelength) was used for vibrational studies of the sp -bonded carbon phase. The resulting spectra recorded at different points at the surface besides the D- and G-band demonstrated a new feature in the range 1328 1332cm , which corresponds to the CVD-deposited nanocrystalline-sized diamonds (Figure 3.9b). The curve shape analysis of this band, i.e. its peak position and width provides information about the size of the CVD-deposited diamond crystallites [30]. With diamond size decreasing from 1000 nm to... 

NMR is not, of course, the only analytical technique used to establish the composition and microstructure of polymeric materials. Others include >66 ultraviolet-visible spectroscopy (UV-Vis), Raman spectroscopy, and infrared (IR) spectroscopy. IR and Raman spectroscopy are particularly useful, when by virtue of cross-linking (see. e.g. Chapter 9), or the presence of rigid aromatic units (see Chapter 4). the material neither melts nor dissolves in any solvent suitable for NMR. The development of microscopy based on these spectroscopic methods now makes such analysis relatively simple (see below). Space precludes a detailed account of these and many other techniques familiar to the organic chemist. Instead we focus for the remainder of the chapter on some of the techniques used to characterize the physical properties of polymeric materials. 

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