Infrared extinction coefficient

In situ infrared reflectance spectroscopy investigation of the oxidation reaction of ethanol appears thus as an efficient method to elucidate some mechanistic aspects of the reaction. However, the quantitative analysis of the reaction products remains difficult due to different parameters the characteristic absorption band may not be monopolar (this is the case for carbon monoxide for example) and the difficulty to obtain a quantitative relationship between infrared extinction coefficients and concentration for reaction products and by-products. 

The crystallinity or the fraction of crystalline material x(c) can be derived from specific volume data, from specific heat data, from infrared extinction coefficient data, from X-ray scattering data, from NMR data or from heat of fusion data. 

A comparison of Eqs. (9.1.37) and (9.1.39) yields a minimum value B(0) >. y/ 3 F (0)/4. The exact value depends on, the ratio of visible-to-infrared extinction coefficients. As increases from zero to larger values, B 0) increases accordingly, and, for sufficiently large a temperature inversion is introduced in the stratosphere. 

Hoffmann, R. W., and G. W. Brindley, 1961. Infrared extinction coefficients of ketones adsorbed on Ca montmorillonite in relation to surface coverage. Clay-organic studies. IV. J. Phys. Chem. 65 443. 

Infrared ellipsometry is typically performed in the mid-infrared range of 400 to 5000 cm , but also in the near- and far-infrared. The resonances of molecular vibrations or phonons in the solid state generate typical features in the tanT and A spectra in the form of relative minima or maxima and dispersion-like structures. For the isotropic bulk calculation of optical constants - refractive index n and extinction coefficient k - is straightforward. For all other applications (thin films and anisotropic materials) iteration procedures are used. In ellipsometry only angles are measured. The results are also absolute values, obtained without the use of a standard. 

The development and adaptation of procedures for the separation, isolation, purification, identification, and analysis of the components of the pyrethrum mixture have been studied and evaluated. Results of studies to determine the molar extinction coefficient of pyrethrin I as well as a gas chromatographic procedure for the determination of pyrethrins are reported. The use of chromatographic separation procedures (including partition, adsorption, gas, and thin-layer chromatography), colorimetry, and infrared spectrophotometry are discussed. 

The separations allowed by the partition column provided a rather pure sample of pyrethrin I, demonstrated by the gas chromatograph and by comparison with known infrared spectra. The purified pyrethrin I was weighed quantitatively and a color test performed to determine the extinction coefficient. The figure obtained from ten runs is 1120, calculated from the formula ... 

Other physical methods were also applied to the elucidation of the isomerism of diazocyanides, e. g., determination of diamagnetic susceptibility, the Faraday effect (optical rotation in a magnetic field), and electronic and infrared spectra. Hantzsch and Schulze measured ultraviolet spectra at a remarkably early date (1895 a). Unfortunately, their results and later work (Le Fevre and Wilson, 1949 Freeman and Le Fevre, 1950) did not allow unambiguous conclusions, except perhaps the observation that the molar extinction coefficients of the band at lowest frequency are consistently larger in all types of (i -compounds Ar — N2 - X than in the corresponding (Z)-iso-mers (Zollinger, 1961, p. 62). 

Chemical methods for structure determination in diene pol3 mers have in large measure been superseded by infrared absorption techniques. By comparing the infrared absorption spectra of polybutadiene and of the olefins chosen as models whose ethylenic structures correspond to the respective structural units, it has been possible to show that the bands occurring at 910.5, 966.5, and 724 cm. are characteristic of the 1,2, the mns-1,4, and the m-1,4 units, respectively. Moreover, the proportion of each unit may be determined within 1 or 2 percent from measurements of the absorption intensity in each band. The extinction coefficients characteristic of each structure must, of course, be known these may be assigned from intensity measurements on model compounds. Since the proportions of the various units depend on the rates of competitive reactions, their percentages may be expected to vary with the polymerization temperature. The 1,2 unit occurs to the extent of 18 to 22 percent of the total, almost independent of the temperature, in free-radical-polymerized (emulsion or mass) poly butadiene. The ratio of trans-1,4 to cfs-1,4, however,... 

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). 

One cm3 of the reactant/product/catalyst mixture was sampled periodically during the reaction for the transmission infrared analysis (Nicolet Magna 550 Series II infrared spectrometer with a MCT detector). The concentrations of reactants and products were obtained by multiplying integrated absorbance of each species by its molar extinction coefficient. The molar extinction coefficient was determined from the slope of a calibration curve, a plot of the peak area versus the number of moles of the reagent in the IR cell. The reaction on each catalyst was repeated and the relative error for the carbamate yield measured by IR is within 5%. 

The palladium phthalocyanine (67), developed by Mitsui Toatsu and Ciba58,59 is one of the leading phthalocyanine infrared absorbers for CD-R (Compact Disk-Rewritable) (see Chapter 9.13). Bulky groups (R) reduce undesirable molecular aggregation, which lowers the extinction coefficient and hence the absorptivity and reflectivity. Partial bromination allows fine tuning of the film absorbance and improves reflectivity. The palladium atom influences the position of the absorption band, the photostability and the efficiency of the radiationless transition from the excited state.58 It is marketed by Ciba as Supergreen.60... 

The analytical data of the catalysts used are given in Table II. The number of B5 sites was determined from infrared measurements and nitrogen adsorption isotherms in the way outlined by van Hardeveld and Montfoort 10). The values found are higher than those mentioned in an earlier paper 24), owing partly to an improvement of the method for determining the extinction coefficient per molecule of nitrogen adsorbed,... 

Emeis, C.A. Determination of integrated molar extinction coefficients for infrared absorption bands of pyridine adsorbed on sohd acid catalysts. J. Catal. 1993,141, 347-354. 

The sodium chloride (NaCl) crystal shows very high absorption and reflectivity in the infrared region, known as the Restrahlen region. The real and imaginary relative dielectric constants at 6000 nm are, respectively, ei = 16.8 and S2 = 91.4. At this wavelength, estimate (a) the refractive index and the extinction coefficient, and (b) the optical density and the reflectivity at normal incidence for a 1 mm thick NaCl sample, (c) If the previous sample is illuminated (at normal incidence) by a beam of intensity Iq at 6000 nm, estimate the intensity of this... 

Prior to 1970 our understanding of the bonding of diatomic molecules to surfaces, and in many cases the type of adsorption (i.e., molecular or dissociative) was almost entirely dependent on indirect experimental evidence. By this we mean that deductions were made on the basis of data obtained from monitoring the gas phase whether in the context of kinetic studies based on gas uptake or flash desorption, mass spectrometry, or isotopic exchange. The exception was the important information that had accrued from infrared studies of mainly adsorbed carbon monoxide, a molecule that lent itself very well to this approach owing to its comparatively large extinction coefficient. 

The first two determinations by radiation absorption require accurate measurements of the extinction coefficients of ozone (a measurement of the absorption efficiency of the incoming radiation at a maximal absorption wavelength) in the ultraviolet and the infrared. Three different principles have been used over the last 20 years to measure the extinction coefficient of ozone in the ultraviolet at 254 nm manometric, decomposition stoichiometry, and gas-phase titration. The manometric method, which is based on pressure measurements of gaseous ozone, requires (in at least one case ) a substantial and somewhat uncertain correction for decomposition and the method of decomposition stoichiometry depends on the pressure change that accompanies the decomposition of ozone to oxygen, 20, 30,. Clyne and Coxon determined ozone... 

The two complexes have absorption maxima at 524.0 nm, with concentration-dependent extinction coefficients. This concentration dependence is thought to result from a concentration-dependent distribution of molecular aggregates. Infrared spectra show only the bands associated with the ligand, the most prominent of which are 3300-3460, 1458, 1412, 1075, 730,682, and 480 cm 1 (KBr disk). Raman bands for the triphenylphosphine complex appear at 180, 124, and 90 cm 1. 

These features make IR spectrometry a potentially strong technique for the characterization of chromatographic peaks. However, compared with UV-vis absorbance, extinction coefficients in IR are rather low, and the amount of analyte needed for IR detection therefore is often larger that the amounts usually injected into a GC or LC. Nevertheless, enhanced sensitivity can be achieved by the Fourier transform (FT) version of the infrared spectroscopy (FTIR) (136). 

First, let us consider infrared studies at cryogenic temperatures as a probe of transitions in polymers. The temperature of the extinction coefficient is usually assumed to have a linear dependence 308). 

The infrared spectrum of partially deuterated polyethylene has been examined as a function of temperature 323). Bands associated with trans-trans (tt) bond pairs and trans-gauche (tg) bonds have been identified so it is possible to follow the changes in these isomers as a function of temperature. As the temperature increased, the intensity of the tg band increased, while the intensity of the tt band decreased. It is hypothesised that the extinction coefficients for the two bands are essentially equal and the nearly constant total intensity of the two bands seems to confirm this hypothesis. Thus it appears that each time a tt sequence disappears a tg sequence is created. Correlations of this infrared result with the intensity of the Raman longitudinal acoustic mode, suggest that the new thermally induced tg sequences occur mainly as point dislocations in the crystal 323). 

H. L. Retcofsky How did you derive the extinction coefficients which you used for determining H.i from the infrared spectra of macerals ... 

Hubert Tschamler They were derived either from mean values observed for model compounds of known structure or from the properties of solvent extracts of coals. In the latter case an accurate value for %H i can be derived by measuring proton spin resonance in solution and this, combined with the optical densities observed in the infrared spectra, gives the specific extinction coefficients. (See J. F. M. Oth, E. de Ruiter and H. Tschamler, Brennstoff-Chem. 42, 378 (1961) also Ref. 7). 

Compared with infrared spectroscopy the NMR method has the advantage that a determination of the number of OH groups does not require any assumptions like constancy of extinction coefficients. On the other hand, NMR has a lower sensitivity and poor resolution. 

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