Spectroscopy extinction coefficient

Time-resolved optical absorption spectroscopy experiments have shown that arenesul-fonyl radicals decay with clean second-order kinetics14 the values of 2 k,/a h where s2 is the extinction coefficient at the monitoring wavelength, increased linearly with decreasing viscosity of the solvent, further indicating that reaction 16 is clearly a diffusion-controlled process. 

Low-temperature, photoaggregation techniques employing ultraviolet-visible absorption spectroscopy have also been used to evaluate extinction coefficients relative to silver atoms for diatomic and triatomic silver in Ar and Kr matrices at 10-12 K 149). Such data are of fundamental importance in quantitative studies of the chemistry and photochemistry of metal-atom clusters and in the analysis of metal-atom recombination-kinetics. In essence, simple, mass-balance considerations in a photoaggregation experiment lead to the following expression, which relates the decrease in an atomic absorption to increases in diatomic and triatomic absorptions in terms of the appropriate extinction coefficients. 

Porra, R.J., Thompson, W.A., and Kriedemann, P.E., Determination of accurate extinction coefficients and simultaneous equations for assaying chlorophylls a and b extracted with four different solvents verification of the concentration of chlorophyll standards by atomic absorption spectroscopy, Biochim. Biophys. Acta, 975,384, 1989. 

Application of Fluorescence Correlation Spectroscopy 145 Table 8.1 Local temperature deviation, extinction coefficient, thermal conductivity. 

The specific surface area of the fresh and used catalysts was measured by nitrogen adsorption method (Sorptometer 1900, Carlo Erba Instruments). The catalysts were outgassed at 473 K prior to the measurements and the Dubinin equation was used to calculate the specific surface area. The acidity of investigated samples was measured by infrared spectroscopy (ATI Mattson FTIR) by using pyridine (>99.5%, a.r.) as a probe molecule for qualitative and quantitative determination of both Bronstcd and Lewis acid sites (further denoted as BAS and LAS). The amounts of BAS and LAS were calculated from the intensities of corresponding spectral bands by using the molar extinction coefficients reported by Emeis (23). Full details of the acidity measurements are provided elsewhere (22). 

The other notable feature of the optical spectroscopy of the lanthanide ions is that their absorption bands generally have very low extinction coefficients, because f-f transitions are... 

The use of electrochemical transmittance spectroscopy in both the UV-visible and IR regions of the spectrum is elegantly shown by the work of Ranjith et al. (1990) who employed an OTTLE cell to study the reduction of benzoquinone, BQ. The authors were the first to report the UV-visible spectrum of BQ2- and to demonstrate the quantitative aspects of the technique by reporting extinction coefficients for the major bands of BQT and BQ2- in both the UV-visible and IR. 

Keywords IR spectroscopy, integral molar extinction coefficients, propene, adsorption, zeolites. 

The density of Bronstcd and Lewis acid sites was determined by IR spectroscopy (Nicolet 710) of adsorbed pyridine, after desorption at 250°C, using the molar extinction coefficients previously obtained by Emeis [11]. The acid strength distribution of selected zeolites was studied by NH3-TPD in an Autochem 2910 Equipment (Micromeritics) coupled to a quadrupole mass spectrometer. First, NH3 was adsorbed at 175°C until saturation and then desorbed by increasing the temperature up to 800°C at a heating rate of 10°C/min. 

Optical activity also manifests itself in small differences in the molar extinction coefficients el and er of an enantiomer toward the right and left circularly polarized light. The small differences in e are expressed by the term molecular ellipticity [9 J = 3300(el — r). As a result of the differences in molar extinction coefficients, a circularly polarized beam in one direction is absorbed more than the other. Molecular ellipticity is dependent on temperature, solvent, and wavelength. The wavelength dependence of ellipticity is called circular dichroism (CD). CD spectroscopy is a powerful method for studying the three-dimensional structures of optically active chiral compounds, for example, for studying their absolute configurations or preferred conformations.57... 

We perform a series of experiments. We purchase a stock of identical plates and prepare several solutions of beetroot juice of varying concentration. One plate is soaked per solution. The chemisorptive bond between the dye and plate is strong, and equilibrium is reached after only a few seconds. The excess juice is decanted off for analysis, e.g. by means of optical spectroscopy and the Beer-Lambert law, provided we know the extinction coefficient s for the juice. 

The kinetics of reactions involving the tributylstannyl radical have been refined by laser flash time-resolved UV spectroscopy. The measured extinction coefficient of the BujSn- radical in benzene was 1620 40 M 1cm 1 at 400 nm, the rate constant of the reaction of the /-butoxyl radical with Bu3SnH was (3.5 0.3) x 108M 1 s 1, and the rate constant for the self-reaction of the Bu3Sn radical was (3.6 0.3) x 109 M s1. S29... 

By analogy with absorption spectroscopy we may identify an extinction coefficient due to scattering with the turbidity r which is defined as ... 

A fundamental unit in spectroscopy (synonymous with molar extinction coefficient) and symbolized by e. It is equal to the absorbanee of light per unit path length and per unit eoncentration. See Absorption Spectroscopy Beer-Lambert Law... 

Fortunately, the mid-IR stretches of the terminal carbonyls of simple carbonyl iodide complexes of Rh and Ir occur in the region 1950 to 2150 cm Their extinction coefficients are sufficiently strong that even in aqueous AcOH, which would not be a solvent of choice for mid-IR spectroscopy, at concentrations in the range of 100s of ppm w/w, the simple Rh or Ir carbonyl iodides can be detected by FTIR with a modest acquisition time. Indeed much of the original IR work to study both Rh and Ir catalysed carbonylation by workers at Monsanto [11, 25] and by Schrod et al. [26] appears to have been carried out using continuous wavelength machines. 

In 1993, UV spectroscopy has been used to clarify the strong interactions of 1,2,5-thiadiazole dioxides with protic solvents. Based on shifts in the maximum from 328 nm to 267 nm, as well as a doubling in the extinction coefficient, it is likely that the adduct II (Equation (1)) is formed in alcoholic media <93JP034i>. 

Electronic spectra (Table 1.1, Fig. 1.2) have been measnred for the orange soln-tions of (RuO ] in aqueous base from 250-600 nm. [212-215, 222], and reproduced [215, 222]. There are two at 460 and 385 nm. [212, 213, 222] or three bands in the visible-UV region, at 460, 385 and 317 nm [214, 215]. These appear to be at the same positions as those for [RuO ] but the intensities and hence the general outline of the two spectra are very different. Woodhead and Fletcher reviewed the published molar extinction coefficients and their optimum values / dm (mol" cm" ) are 1710 for the 460 nm. band, 831 for the 385 nm. band and 301 for the 317 nm. band - the latter band was not observed by some workers [214]. The distinctive electronic spectrum of ruthenate in solution is useful for distinguishing between it, [RuO ]" and RuO [212, 222]. Measurements of the electronic spectra of potassium ruthenate doped in K CrO and K SeO and of barium ruthenate doped into BaSO, BaCrO, and BaSeO (in all cases the anions of these host materials are tetrahedral) indicate that in that these environments at least the Ru is tetrahedrally coordinated. Based on this evidence it has been suggested that [RuO ] in aqueous solution is tetrahedral [RuO ] rather than franx-[Ru(0H)3(0)3] [533, 535]. Potential modulated reflectance spectroscopy (PMRS) was used to identify [RuO ] and [RuO ] " in alkaline aqueous solutions during anodic oxidation of Ru electrodeposited on platinum from [Ru3(N)Clg(H30)3] [228]. 

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