Reflection UV spectroscopy

The table 3 give the UV-wavelength of protonated methylated benzene molecules as compared to their basicity relative to p-xylene. The presence of UV-bands at values very similar to those of table 3 upon adsorption in zeolites suggest that protonation of these compounds may occur (59). The study carried out by diffuse reflectance UV-spectroscopy... 

The shifts in wavenumbers indicate a change in the electronic structure of aromatics adsorbed compared to the liquid or gas phase. Such modiflcadons in adsorbates have been rather extensively studied in the case of benzene using diffuse reflectance UV spectroscopy (77), UV-visible transmission microscope spectrophotometry (78) or laser raman spectroscopy (79). All the results suggest the formation of a complex between the cation and the it electrons of the aromatic ring. Hindrance in mobility compared to that of benzene in the solid state have been observed (78). 

Weckhuysen and Schoonheydt [100, 199] conducted systematic studies of the preparation of Cr-containing zeohtes. These authors employed diffuse reflectance UV spectroscopy (DRS) and ESR spectroscopy. For a comparative investigation, they loaded various zeolites (X, Y, [Ga]Y and MOR-type zeolites) not only by conventional ion exchange or impregnation-incipient wetness techniques but also via soHd-state ion exchange with CrClj 6H2O. After calcination of differently prepared samples at 823 K, similar DRS spectra were obtained (cf. Fig. 58). 

Langmuir-Blodged films have been deposited on many different substrates. The substrates used include different types of glass (such as quartz for UV-visible spectroscopy) CaF2 plates for transmission infrared spectroscopy silicon, germanium, and ZnSe plates for internal reflection infrared spectroscopy. For electrochemical applications, LB films... 

The quantification of the extra-framework titanium species in titanium silicalites of MFI structure, TS-1, was performed using either XANES at the Ti K-edge or XPS Ti (2p) photolines. In addition, two different framework sites, [Ti(OH)(OSi)3] and [Ti(OSi)4], were characterized in dehydrated samples using Diffuse Reflectance UV-visible, multiple scattering analysis of EXAFS, H and Si NMR spectroscopies. 

The mere exposure of diphenyl-polyenes (DPP) to medium pore acidic ZSM-5 was found to induce spontaneous ionization with radical cation formation and subsequent charge transfer to stabilize electron-hole pair. Diffuse reflectance UV-visible absorption and EPR spectroscopies provide evidence of the sorption process and point out charge separation with ultra stable electron hole pair formation. The tight fit between DPP and zeolite pore size combined with efficient polarizing effect of proton and aluminium electron trapping sites appear to be the most important factors responsible for the stabilization of charge separated state that hinder efficiently the charge recombination. 

The most notable feature of these intrazeolite photooxygenations (Fig. 30) is that the oxygen CT band experiences a dramatic bathochromic shift in comparison to solution. This was detected initially by recording the product growth as a function of irradiation wavelength (laser reaction excitation spectrum)98,110 and was later verified by direct observation using diffuse reflectance UV-Vis spectroscopy.111 For example, 2,3-dimethyl-2-butene CT-absorbance is shifted to lower energy by more than 300 nm... 

The IR and Raman spectra of benzotriazole, benzotriazole anion and its Cu(I) complex have been measured. The characteristic peaks in the IR spectrum of the triazole moiety in benzotriazole anion occur at 1163 cm , 1134 cm , and 1115 cm . A broad band with a main peak at 1151 cm occurs in the spectrum of the Cu(I)-BTA complex <85JST(l00)57i>. The chemisorption of benzotriazole on clean copper and cuprous oxide surfaces is investigated by combining XPS, UV-PE and IR reflection absorption spectroscopy (IRAS). Coordination geometry including the triazole-... 

The Ti environment in trimethylsilylated Ti-MCM-41 catalysts with different degrees of silylation was studied by means of diffuse reflectance UV-vis spectroscopy. The UV-vis spectra of trimethylsilylated samples are compared with the calcined material in figure 6. 

M(lI)AlSn-LDHs with M(II) being Mg, Ni or Co were synthesized by a coprecipitation method. The influence of Sn on the thermal transformations and redox properties were investigated in detail using XRD, TG/DTA, SEM, TPR, 1 l9Sn-MAS NMR and UV-visible diffuse-reflectance (DR) spectroscopy methods. Some of these samples calcined at 450 °C were tested as catalysts in the partial oxidation of methanol (POM) reaction. In this paper we discuss briefly the effect of Sn-incorporation on the structural features and reducibility of CoAI-LDH. The catalytic performance of Co-spinel microcrystallites derived from CoAl-, and CoAlSn-LDHs was also evaluated. 

This article shows how the evanescent wave can be used with advantage for spectroscopic purposes in the field of biomedical engineering. Three types of spectroscopy can be done with the evanescent wave in the UV-VIS range of the spectrum (a) attenuated total reflection (ATR) spectroscopy, which is well known in the infrared (b) the excitation of Raman scattering with the evanescent wave and (c) the excitation of fluorescence with the evanescent wave. The first two types will be discussed in this article the third is discussed for example by Hirschfeld U) and more recently by Watkins and Robertson (2). But before going into details a historical review may be of some interest. 

To avoid these two difficulties for our analysis, we used reflectivity spectra of thin, high-quality crystals, with surface structures subtracted out to recover the bulk reflectivity of a perfect semiinfinite crystal. Since this problem and its inherent difficulties are often ignored, we describe below our approach, up to the final application to UV spectroscopy, in order to point out the source of discrepancies originating either from the sample spectra or from the theoretical approximations. 

Nevertheless, the mere knowledge of r(co) 2 is not sufficient to provide the two parameters v(co) and k(u)) both reflection and transmission spectra are needed. This is the main reason that the KK transformation is used for reflectivity spectra, as we summarize below in application to our problem of UV spectroscopy. 

Optical Accessory Design for Diffuse Reflectance UV-vis-NIR Spectroscopy... 

Biirgi (2005) described equipment combining attenuated total reflection IR with reflectance UV-vis spectroscopy. A fiber optical probe was positioned parallel to the surface normal of the internal reflection element in front of a fused silica window in the reactor. The distance from the probe to the catalyst layer was about 4 mm. A second fiber optical arrangement allowed simultaneous acquisition of transmission UV-vis spectra of the effluent liquid from the reactor cell. All measurements were performed with the catalyst at 303 K. 

Lezna and coworkers (Juanto et al., 1994 Lezna et al., 2003) combined diffuse reflectance UV-vis spectroscopy with cyclovoltammetry, using a specially designed spectrometer with an optical multichannel analyzer. 

Diffuse reflectance UV-vis spectroscopy was applied in electrocatalysis by El Mouahid et al. (1998), who followed the electropolymerization of a cobalt porphyrin complex on a vitreous carbon electrode. The thin polymer... 

As previously emphasized in the discussion of quantitative methods employing UV spectroscopy, the accuracy of the results is strongly dependent on the selection or determination of an absorptivity value that reflects the spectral characteristics of the lignin actually being measured. 

The base-base interaction between two polymer chains is well reflected by a hypochromic effect, which can be studied by UV spectroscopy in solution. For a series of compounds, UV measurements were done and the results discussed and compared with those of emission spectroscopy. 

The adsorption property was measured by a static method at 30 °C with a conventional volumetric apparatus as well as by the temperature programmed desorption (TPD) method. The details of the pretreatment and adsorption procedures were shown in Results and Discussion section. Metal-loaded zeolite samples were characterized by XRD, diffuse reflectance UV-Vis spectroscopy (DRS) and electron spin resonance (ESR). 

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