Raman diagnostics

Laser Raman diagnostic teclmiques offer remote, nonintnisive, nonperturbing measurements with high spatial and temporal resolution [158], This is particularly advantageous in the area of combustion chemistry. Physical probes for temperature and concentration measurements can be debatable in many combustion systems, such as furnaces, internal combustors etc., since they may disturb the medium or, even worse, not withstand the hostile enviromnents [159]. Laser Raman techniques are employed since two of the dominant molecules associated with air-fed combustion are O2 and N2. Flomonuclear diatomic molecules unable to have a nuclear coordinate-dependent dipole moment caimot be diagnosed by infrared spectroscopy. Other combustion species include CFl, CO2, FI2O and FI2 [160]. These molecules are probed by Raman spectroscopy to detenuine the temperature profile and species concentration m various combustion processes. 

Figure 15 FT-Raman spectra of fake ivory specimens (a) carved X ctorian bangle, (b) large bangle, (c) small bangle, (d) cal. The absence of the characteristic proteinaceous features in true ivory near 1650 and 1450 cm and the strong phosphate mode near 960 cm" should be noted. Also, the presence of the aromatic ring bands at 3060, 1600, and 1000 cm" in (b) and (d) indicate a polystyrene resin content, whereas the carbonyl stretching band at 1725 cm" in all fake specimens indicates the presence of poly(methyl methacrylate). In the cat specimen, the band at 1086 cm uniquely identifies a calcite additive in the specimens of imitation ivory studied. (Reproduced with permission from HGM Edwards, DW Farwell. Ivory and simulated ivory artifacts Fourier-transform Raman diagnostic study. Spectrochimica Acta, Part A, 51 2073-2081. 1995, Elsevier Science B.V.)...

Figure 18 FT-Raman stackplot spectra of scrimshaw specimens (a) hollow sperm whale tooth, (b) solid sperm whale tooth, (c) whalebone staybusk, and (d) spill vase/quill pen holder. Minor spectroscopic differences confirm the whalebone origin of the staybusk. The modern resin composition of the spill vase/quill pen holder is also unambiguously identified from the aromatic ring stretching bands at 3060 cm and 1600 cm". (Reproduced with permission from HGM Edwards, DW Farwell, T Seddon, JKF Tait. Scrimshaw Real or Fake An FT-Raman Diagnostic Study. Journal of Raman Spectroscopy, 26 623-628. 1995. John Wiley and Sons Ltd.)...

HGM Edwards, DW Farwell. Ivory and simulated ivory artefacts an FT-Raman diagnostic study. Spectrochim Acta A 51 2073-2081, 1995. 

Figure 3 Ivory cat, which was identified spectroscopically as a modern limitation composed of poly(methyl methacrylate) and polystyrene resins with added calcite to give the texture and density of ivory. Reproduced with permission from Edwards HGM and Farwell DW, Ivory and simulated ivory arte cts Fou-rier-transform Raman diagnostic study, Spectrochimica Acta, Part A, 51 2073-2081 1995, Elsevier Science B. V. (See Colour Plate 3).

Fig. 14.7. Multipass cell for sensitive Raman diagnostics of molecular gases [14.35]...

Plenary 15. B Scluader et al, e-mail address beriilrard.scluader uni-essen.de (NIR-FTRS). A review of the use of Raman spectroscopy in medical diagnostics. Its possibilities, limitations and expectations. Emphasizes the need for a library of reference spectra and the applications of advanced analysis (chemometry) for comparing patient/library spectra. 

Eckbreth A C 1988 Nonlinear Raman spectroscopy for combustion diagnostics J. Quant. Spectrosc. Radlat. Transfer 40 369-83... 

Shim M G and Wilson B C 1997 Development of an in vivo Raman spectroscopic system for diagnostic applications J. Raman Spectrosc. 28 131-42... 

Biosensors (qv) and DNA probes ate relatively new to the field of diagnostic reagents. Additionally, a neat-infrared (nit) monitoring method (see Infrared TECHNOLOGY AND RAMAN SPECTROSCOPY), a teagenfless, noninvasive system, is under investigation. However, prospects for a nit detection method for glucose and other analytes ate uncertain. 

The Raman spectrum of aqueous mer-cury(I) nitrate has, in addition to lines characteristic of the N03 ion, a strong absorption at 171.7 cm which is not found in the spectra of other metal nitrates and is not active in the infrared it is therefore diagnostic of the Hg-Hg stretching vibration since homonuclear diatomic vibrations are Raman active not infrared active. Similar data have subsequently been produced for a number of other compounds in the solid state and in solution. 

These models are designed to define the complex entrance effects and convection phenomena that occur in a reactor and solve the complete equations of heat, mass balance, and momentum. They can be used to optimize the design parameters of a CVD reactor such as susceptor geometry, tilt angle, flow rates, and others. To obtain a complete and thorough analysis, these models should be complemented with experimental observations, such as the flow patterns mentioned above and in situ diagnostic, such as laser Raman spectroscopy. 

Here, selected, more established laser diagnostic techniques will only be briefly named with their principal area of application in combustion measurements, but not further described details on these and other methods can be found in the above-mentioned literature and references cited therein. Workhorse techniques in combustion diagnostics include Raman and Rayleigh... 

Culha M., Stokes D., Allain L.R., Vo-Dinh T., Surface-enhanced Raman scattering substrate based on a self-assembled monolayer for use in gene diagnostics, Anal. Chem. 2003 75 6196-6201. 

Raman spectroscopy is primarily useful as a diagnostic, inasmuch as the vibrational Raman spectrum is directly related to molecular structure and bonding. The major development since 1965 in spontaneous, c.w. Raman spectroscopy has been the observation and exploitation by chemists of the resonance Raman effect. This advance, pioneered in chemical applications by Long and Loehr (15a) and by Spiro and Strekas (15b), overcomes the inherently feeble nature of normal (nonresonant) Raman scattering and allows observation of Raman spectra of dilute chemical systems. Because the observation of the resonance effect requires selection of a laser wavelength at or near an electronic transition of the sample, developments in resonance Raman spectroscopy have closely paralleled the increasing availability of widely tunable and line-selectable lasers. 

Vo Dinh, T. Stokes, D. L., Surface enhanced Raman scattering for biomedical diagnostics, Biomedical Photonics Handbook, Vo Dinh, T., Ed. CRC Press, Boca Raton, EL, 2003, 64.1 64.39... 

The experimental techniques described above of charge—discharge and impedance are nondestructive. Tear-down analysis or disassembly of spent cells and an examination of the various components using experimental techniques such as Raman microscopy, atomic force microscopy, NMR spectroscopy, transmission electron microscopy, XAS, and the like can be carried out on materials-spent battery electrodes to better understand the phenomena that lead to degradation during use. These techniques provide diagnostic techniques that identify materials properties and materials interactions that limit lifetime, performance, and thermal stabiity. The accelerated rate calorimeter finds use in identifying safety-related situations that lead to thermal runaway and destruction of the battery. 

If spectral diagnostics are required the IR spectrum (like the Raman spectrum) offers a host of well-documented diagnostic spectral data that can be used to identify and characterize materials from basic principles. This is ideal for confirming material identity and for determining the presence of contaminants, even at low concentrations. 

NIR Vibrational overtones and combination bands Very high S/N Relatively low sensitivity facilitates minimum sample preparation Most popular on-line technique, but not as sensitive or diagnostic as IR and Raman. Sensitivity to physical as well as chemical status can be a problem or an opportunity, depending on application... 

---