Spectroscopic UV-Vis

Syntheses, electrochemical and spectroscopic (UV, Vis, NIR, and EPR) properties of [ MoCl(Tp )(NO) 2( -i-L)] containing two-redox active Mo(Tp ) units linked by a conjugated bridging ligand L have been reported by McCleverty and others. Some of these complexes exhibit intense, redox-switchable absorbance in the near-IR region.75... 

The sensitivities of particular spectroscopic teclmiques to specific chemical features are described more fully in tire next section. Perhaps tire most common and versatile probes of reaction dynamics are time-resolved UV-vis absorjDtion and fluorescence measurements. Wlren molecules contain cliromophores which change tlieir stmcture directly or experience a change of environment during a reaction, changes in absorjDtion or fluorescence spectra can be expected and may be used to monitor tire reaction dynamics. Altliough absorjDtion measurements are less sensitive tlian fluorescence measurements, tliey are more versatile in tliat one need not rely on a substantial fluorescence yield for tire reactants, products or intennediates to be studied. 

The equilibrium constants obtained using the metal-ion induced shift in the UV-vis absorption spectrum are in excellent agreement with the results of the Lineweaver-Burke analysis of the rate constants at different catalyst concentrations. For the copper(II)ion catalysed reaction of 2.4a with 2.5 the latter method gives a value for of 432 versus 425 using the spectroscopic method. 

Molar absorptivity when measured at X x is cited as e ax It is normally expressed without units Both X x and Cmax are affected by the solvent which is therefore included when reporting UV VIS spectroscopic data Thus you might find a literature reference expressed m the form... 

With this as background, we will now discuss spectroscopic techniques individually. NMR, IR, and UV-VIS spectroscopy provide complementary information, and all are useful. Among them, NMR provides the information that is most directly related to molecular- structure and is the one we ll examine first. 

Further structural information is available from physical methods of surface analysis such as scanning electron microscopy (SEM), X-ray photoelectron or Auger electron spectroscopy (XPS), or secondary-ion mass spectrometry (SIMS), and transmission or reflectance IR and UV/VIS spectroscopy. The application of both electroanalytical and surface spectroscopic methods has been thoroughly reviewed and appropriate methods are given in most of the references of this chapter. 

The most suitable spectroscopic method for food colorants is UV-Vis absorption spectrometry. To quantify the concentration of a food colorant the light transmission, T, must be measured ... 

Endo et al. [96] prepared AuPt, AuPd, and PtPd bimetallic nanoparticles with 2 nm in particle size in order to investigate catalytic activity for reduction of p-nitrophenol in water. The binary features of the nanoparticles were characterized by UV-Vis spectroscopic measurements. 

Sets of spectroscopic data (IR, MS, NMR, UV-Vis) or other data are often subjected to one of the multivariate methods discussed in this book. One of the issues in this type of calculations is the reduction of the number variables by selecting a set of variables to be included in the data analysis. The opinion is gaining support that a selection of variables prior to the data analysis improves the results. For instance, variables which are little or not correlated to the property to be modeled are disregarded. Another approach is to compress all variables in a few features, e.g. by a principal components analysis (see Section 31.1). This is called... 

A high specific interfacial area and a direct spectroscopic observation of the interface were attained by the centrifugal liquid membrane (CLM) method shown in Fig. 2. A two-phase system of about 100/rL in each volume is introduced into a cylindrical glass cell with a diameter of 19 mm. The cell is rotated at a speed of 5000-10,000 rpm. By this procedure, a two-phase liquid membrane with a thickness of 50-100 fim. is produced inside the cell wall which attains the specific interfacial area over 100 cm. UV/VIS spectrometry, spectro-fluorometry, and other spectroscopic methods can be used for the measurement of the interfacial species and its concentration as well as those in the thin bulk phases. This is an excellent method for determining interfacial reaction rates on the order of seconds. 

Time-resolved spectroscopic techniques are important and effective tools for mechanistic photochemical studies. The most widely used of these tools, time-resolved UV-VIS absorption spectroscopy, has been applied to a variety of problems since its introduction by Norrish and Porter almost 60 years ago. Although a great deal of information about the reactivity of organic photochemical intermediates (e.g., excited states, radicals, carbenes, and nitrenes) in solution at ambient temperatures has been amassed with this technique, only limited structural information can be extracted from... 

Further studies were carried out with halocarbene amides 34 and 357 Although again no direct spectroscopic signatures for specifically solvated carbenes were found, compelling evidence for such solvation was obtained with a combination of laser flash photolysis (LFP) with UV-VIS detection via pyridine ylides, TRIR spectroscopy, density functional theory (DFT) calculations, and kinetic simulations. Carbenes 34 and 35 were generated by photolysis of indan-based precursors (Scheme 4.7) and were directly observed by TRIR spectroscopy in Freon-113 at 1635 and 1650 cm , respectively. The addition of small amounts of dioxane or THF significantly retarded the rate of biomolecular reaction with both pyridine and TME in Freon-113. Also, the addition of dioxane increased the observed lifetime of carbene 34 in Freon-113. These are both unprecedented observations. 

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