Ultraviolet-visible reflectance

Heath and coworkers have recently reported the observation of a reversible, room-temperature metal-non-metal transition in organically-functionalized silver particle monolayers. A useful parameter for characterizing these monolayers is the quantity [d/D], where d is the interparticle separation, as measured between particle centers, and D is the particle diameter (c.f. Fig. 4). The ultraviolet-visible reflectance spectrum from a Langmuir layer of 40 A diameter silver particles, collected in-situ as the film is compressed, is shown in Fig. 13. Upon initial compression, the film becomes more reflective (see (1), (2), and (3) in Fig. 13). The final reflectance spectrum is similar to that reported for thin, metallic silver films ((4) and (5) in Fig. 13) and indicates conclusively that the Langmuir film has finally become metallic. 

Jones, D. H. and Hinman, A. S., Thin-layer ultraviolet visible reflectance spectroelectrochemislry with a spinning-grating monochromator. Can. J. Chem., 68, 2234, 1990. 

Similar reflection plates are used for recording ultraviolet-visible and Raman spectra of matrix isolated molecules, although the traditional beam path passing through transparent quartz windows is more frequently used in UV spectrometers. Sapphire rods, which are placed in the spectrometer cavity, are applied as targets in matrix esr studies. 

Ultraviolet-visible (UV-vis) diffuse reflectance spectra of supported WOx samples and standard W compounds were obtained with a Varian (Cary 5E) spectrophotometer using polytetrafluoroethylene as a reference. The Kubelka-Munk function was used to convert reflectance measurements into equivalent absorption spectra [12]. Spectral features of surface WOx species were isolated by subtracting from the W0x-Zr02 spectra that of pure Z1O2 with equivalent tetragonal content. All samples were equilibrated with atmospheric humidity before UV-vis measurements. 

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. 

The intensities of diffuse reflectance and fluorescence are both distributed over the solid angle according to Lambert s cosine-law. An ultraviolet-visible (UV/VIS)-... 

The progressive increase in the extent of POM reduction, as evidenced by the ultraviolet visible diffuse reflectance (UV-vis DR) spectra of catalysts downloaded after different reaction times during catalyst equilibration. 

Molecular absorption spectroscopy deals with measurement of the ultraviolet-visible spectrum of electromagnetic radiation transmitted or reflected by a sample as a function of the wavelength. Ordinarily, the intensity of the energy transmitted is compared to that transmitted by some other system that serves as a standard. 

Figure 10.2 Absorption spectra of Fe(III) oxides in the ultraviolet-visible region (left) and visible-near-infrared region (right) (from Sherman Waite, 1985). (a) Goethite (b) lepidocrocite (c) maghemite and (d) hematite. Measured reflectance spectra were converted into absorption spectra by applications of the Kebulka-Munk function. The vertical bars indicate band positions (listed in table 10.2).

The simultaneous application of EPR/ultraviolet-visible diffuse reflectance spectroscopy (UV-vis-DRS)/online gas chromatography (GC) to characterize working catalysts was realized a few years ago 14), and laser-Raman spectroscopy has recently been coupled with these to provide the first such simultaneous application of three techniques 15). 

The optical properties of ceramics are useful in the ultraviolet, visible, and infrared ranges of the electromagnetic spectrum, and one key quantity used to describe the optical property of a material is the refractive index, which is a function of the frequency of the electromagnetic radiation. Other quantities used to characterize optical performance are absorption, transmission, and reflection these three properties sum to unity and are also frequency dependent. The last three properties govern many aspects of how light interacts with materials in windows, lenses, mirrors, and filters. In many consumer, decorative, and ornamental applications, the esthetic qualities of the ceramic, such as color, surface texture, gloss, opacity, and translucency, depend critically on how light interacts with the material. 

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