Optical fingerprints

Optical methods monitor the optical absorption/emission/scattering of a gas species at defined optical wavelengths. The distribution of this optical absorption/emission with wavelength provides an optical fingerprint for any gas species present, and the magnitude typically shows the concentration. 

With a prism and a telescope that he manufactured by himself, he discovered numerous black lines in the spectrum of sunlight thrown by a prism. He made use of these lines as wavelength markers when he was developing his new lenses. Subsequently they would be recognized as optical fingerprints for identifying individual elements whose atoms absorbed only certain wavelengths from the sun. Soon after, he became one of the world s premier scientific instrument makers. ... 

In conclusion RAIRS, which affords high spectral resolution, is a very versatile nondestructive optical technique which does not depend on a vacuum environment. Vibrational spectra also serve as characteristic fingerprints for adsorbate molecules, adsorption configurations, and structures on metallic and dielectric substrates. Extension to include dielectric substrates opened new fields of application in polymer and biochemical research. 

Techniques for differentiating between amorphous and crystalline are (i) sharp melting point, (ii) sharp peaks in the solid state infrared fingerprint region, (iii) optical birefringence observed when solid is viewed in a phase contrast microscope and (iv) sharp peaks in the powder X-ray diffraction pattern. 

Optical absorption-based correlation spectroscopy is a means of selectively detecting, or "fingerprinting", gases, in this work, of industrial importance. Optical correlation spectroscopy methods of gas detection are... 

However, further analysis of the behavior of the system in LC cells cast doubt on this interpretation. First, while intuitively attractive, the idea that relaxation of the polarization by formation of a helielectric structure of the type shown in Figure 8.20 would lower the free energy of the system is not correct. Also, in a thermodynamic helical LC phase the pitch is extremely uniform. The stripes in a cholesteric fingerprint texture are, for example, uniform in spacing, while the stripes in the B2 texture seem quite nonuniform in comparison. Finally, the helical SmAPF hypothesis predicts that the helical stripe texture should have a smaller birefringence than the uniform texture. Examination of the optics of the system show that in fact the stripe texture has the higher birefringence. 

C.2. Mass Spectrometry. Like optical emission spectroscopy, mass spectrometry offers the ability to fingerprint and identify individual species in a plasma discharge or products in the effluent from a plasma reactor. Its most common application is the latter, and a diagram for effluent monitoring by... 

Due to the difficulties in interpretation and the sensitivity of vibrations in the fingerprint and skeletal regions to structural alterations, the application of ROA to stereochemical problems remains limited. However, the recent advances in experimental techniques and theoretical descriptions are promoting increased research activity in ROA. Especially in aqueous solution, where VCD signals are obscured by the solvent and in low frequency regions, in which VCD spectra are not yet available, Raman optical activity remains a promising tool for stereochemical investigations. 

Albertidine, isolated from Leontice Albertii Rgl. (196,197), is a crystalline, optically active tribase. There are IR absorption bands for a trani-quinolizidine system at 2750 and 2793 cm and a six-membered lactam carbonyl at 1640 cm The absorption in the fingerprint region is similar to that of matrine. The mass spectrum of albertidine is characterized by ion peaks at miz 247 (M -1), 219, 205, 192, 177, 150, 137, 98, and 96 which are typical for matrine alkaloids (209). On the basis of spectroscopic data and taking into account the tranj-quinolizidine band in the IR spectrum, the probable structure 182, with rings A/B-trans, was proposed. 

A major advantage of infrared absorption spectroscopy derives from the characteristic fingerprints associated with infrared-active molecules. On the other hand, interferences from common atmospheric components such as C02 and HzO are significant, so that the sensitivity and detection limits that can be obtained are useful primarily for polluted urban air situations. For atmospheric work, long optical path lengths are needed. 

A note of caution is necessary when deahng with these materials. It is not trivial to distinguish between CuInS(Se)2 and some phases of Cu—S(Se). Diffraction and optical properties may be similar. Elemental analysis is particularly important to verify inclusion of indium in the films and in the correct ratio. A fingerprint of the chalcopyrite XRD is the presence of a weak peak at 26 = 17-18°, corresponding to the (101) chalcopyrite reflection. This is often not seen, although this could be either because the deposit is not chalcopyrite or because weak peaks are usually not seen in nanocrystaUine materials with particularly small crystal size. 

Since the films are read optically, they should be kept free of dirt, scratches, and fingerprints. 

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