Reflectance technique

Spectrophotometer Works, /. Chem. Educ. 1979, 56, 681-684. Consult the following sources for more information about reflectance techniques for IR spectroscopy. 

An additional advantage to neutron reflectivity is that high-vacuum conditions are not required. Thus, while studies on solid films can easily be pursued by several techniques, studies involving solvents or other volatile fluids are amenable only to reflectivity techniques. Neutrons penetrate deeply into a medium without substantial losses due to absorption. For example, a hydrocarbon film with a density of Ig cm havii a thickness of 2 mm attenuates the neutron beam by only 50%. Consequently, films several pm in thickness can be studied by neutron reflecdvity. Thus, one has the ability to probe concentration gradients at interfaces that are buried deep within a specimen while maintaining the high spatial resolution. Materials like quartz, sapphire, or aluminum are transparent to neutrons. Thus, concentration profiles at solid interfaces can be studied with neutrons, which simply is not possible with other techniques. 

The single most severe drawback to reflectivity techniques in general is that the concentration profile in a specimen is not measured directly. Reflectivity is the optical transform of the concentration profile in the specimen. Since the reflectivity measured is an intensity of reflected neutrons, phase information is lost and one encounters the e-old inverse problem. However, the use of reflectivity with other techniques that place constraints on the concentration profiles circumvents this problem. 

A wide variety of in situ techniques are available for the study of anodic hhns. These include reflectance, eUipsometry, X-ray reflectivity, and SXRD. X-ray reflectivity can be used to study thick surface layers up to 1000 A. The reflectance technique has been used to study oxide growth on metals, and it yields information on oxide thickness, roughness, and stoichiometry. It the only technique that can give information on buried metal-oxide interfaces. It is also possible to get information on duplex or multiple-layer oxide hhns or oxide hhns consisting of layers with different porosity. Films with thicknesses of anywhere from 10 to 1000 A can be studied. XAS can be used to study the chemistry of dilute components such as Cr in passive oxide hhns. 

The three most commonly applied external reflectance techniques can be considered in terms of the means employed to overcome the sensitivity problem. Both electrically modulated infrared spectroscopy (EMIRS) and in situ FTIR use potential modulation while polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) takes advantage of the surface selection rule to enhance surface sensitivity. 

The hexafluoroargentate(III) anion was first obtained as the CS2K salt by Hoppe and Homann [26), who fluorinated a 2 1 1 mixture of CsCl, KC1, and AgNC>3 at 300 °C. A moment of 2.6 B.M. was reported for the product, and the electronic spectrum was studied by Allen and Warren (9), using the diffuse reflectance technique. 

With the exception of single-crystal transmission work, most solids are too opaque to permit the conventional use of ultraviolet/visible (UV/VIS) electronic spectroscopy. As a result, such work must be performed through the use of diffuse reflection techniques [8-10]. Important work has been conducted in which UV/VIS spectroscopy has been used to study the reaction pathways of various solid state reactions. Other applications have been made in the fields of color measurement and color matching, areas which can be of considerable importance when applied to the coloring agents used in formulations. 

In an extension of the diffuse reflectance technique, DR has been used to... 

Refiny product (copper), 7 671 Reflectance, of ODRs, 14 858-859 Reflectance spectrophotometry, 9 232 Reflectance techniques, in infrared spectroscopy, 14 230-232 Reflectancy, 7 305... 

Chlordecone causes a number of neurotoxic responses in humans and animals exposed to sufficiently high levels. Tremor that is accentuated by intentional acts, sustained postural movement, anxiety, or fatigue has been observed in workers exposed to high levels of chlordecone. Tremorograms have been used to objectively assess the tremor associated with chlordecone exposure in humans (Taylor et al. 1978). An infrared reflection technique and oculography have been used to assess the oculomotor disturbances caused by chlordecone (Taylor et al. 1978). Standard tests for memory and intelligence can be used to determine the presence of encephalopathy, but in the absence of baseline preexposure levels for individuals, subtle changes may be difficult to detect. 

Vaidyanathan et al. performed a critical evaluation of models developed for an industrial submerged bioprocess for antibiotic production.56 Both transmission and reflection techniques were employed on a number of reactions. Oil and tylosin were the analytes followed throughout the reaction. 

The ability to recover monolayers and subject them to meaningful analysis has become practical only in recent years because of the development of new methods of trace analysis. High-performance liquid chromatography and vapor phase chromatography allow separation and identification of such small quantities (54a). Attenuated total reflectance techniques for infrared analysis (56) and field desorption mass spectrometry (68) have been applied to the trans-... 

Most high resolution diffractometry is done in reflection 111-V and 11-Vl materials are too absorbing to use conveniently in transmission and, in any case, reflection techniques provide information only from the relevant surface region. 

Two new ways of automating sample preparation have been commercially exploited firstly the infra-red reflectance techniques, which avoid much of the sample pretreatment required for conventional analysis, and, secondly, robotics, to fully automate or mechanize manual techniques. 

Typical examples of its application to processes of interest for atmospheric chemistry are the measurement of the kinetics of the reaction of the vinoxy radical with 02 (Zhu and Johnston, 1995) and the kinetics of the C2H5 + C2H5 and C2H502 + C2H502 reactions (Atkinson and Hudgens, 1997). In addition, it has been shown to be useful for probing surface processes as well when combined with total internal reflection techniques (Pipino et al., 1997). 

In the diffuse reflectance technique (Fig. 14.2d), light scattered by a thick layer of particles is directed by the integrating sphere to a detector. Absorption... 

The first tests of this proposed method have been encouraging. On the basis of comparisons between rainfall rates measured with the differential reflectivity technique and with a network of rain gauges, Seliga et al. (1981) concluded that these first measurements of rainfall using the ZDR technique support the theoretical expectations... that rainfall rate measurements with radar can be made with good accuracy. So it may yet be possible to accurately measure rainfall with radar—provided that measurements are made with two orthogonally polarized beams. This exemplifies one of the principal themes of this book scattered polarized radiation contains information that may be put to good use. 

Seliga, T. A., V. N. Bringi, and H. H. Al-Khatib, 1981. A preliminary study of comparative measurements of rainfall rate using the differential reflectivity technique and a raingauge network,./ Appl. Meteorol., 20. 1362- 1368. 

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