Decadic molar extinction

Light Absorption by Chemical Species Molar Extinction Coefficients Illustrative Example 15.1 Determining Decadic Molar Extinction Coefficients of Organic Pollutants Chemical Structure and Light Absorption The Fate of Excited Chemical Species Quantum Yields... 

Determining Decadic Molar Extinction Coefficients of Organic Pollutants... 

Calculate the decadic molar extinction coefficients of nitrobenzene for the wavelengths indicated above. 

How is the decadic molar extinction coefficient, ,(/l), of a given compound defined What is described by the decadic light absorption or light attenuation coefficient,... 

The absorption maxima in Figure 1, which shows the decadic molar extinction coefficient plotted against wavelength, are at 5800, 6300, 7000, 7400, and 8200 A. The determination of the maximum for methanol by Adams, et al. (1) is in close agreement with our value of 6300 A. that of Grossweiner, et. al. (17) for ethanol by flash photolysis is in satisfactory agreement with our value of 7000 A. It is immediately apparent that the maximum exhibits a red-shift with decrease in the static dielectric con-... 

Figure 1. The absorption spectra of the solvated electron in the aliphatic alcohols at 23°C. The ordinate gives the decadic molar extinction coefficient.

This law can also be given in decadic form, using the decadic molar extinction coefficient s ... 

Electronic Transitions. Since formaldehyde (H2C0) is the simplest carbonyl compound, the CO ir +- n electronic transition of the carbonyl compounds will be briefly described using the formaldehyde transition as the prototype. The lowest singlet state of the CO chromophore of an unconjugated carbonyl can be produced by one-photon absorption of light between 360 and 240 rim (46). This electronic transition is weak, with typical maximum decadic molar extinction coefficient (e) of less than 2 x 10 liters/mol cm. This transition corresponds to the well-known electric-dipole-forbidden vibronically allowed X A ... 

Here /g is the intensity of incident monochromatic radiation, I is the intensity of radiation at a distance I cm, and e is the decadic molar extinction coefficient of an absorbing species (concentration, c mole. 1 ). This law is strictly valid only if molecular interactions are unimportant at all concentrations. Deviations occur for a variety of reasons this means that the validity of the law should be checked under the particular experimental conditions. An initial determination of the absorption spectrum of the compound under investigation is obligatory. This produces immediate qualitative information, particularly about the usefulness of the source of radiation. Banded, diffuse or continuous spectra give direct information about the complexity and variety of primary processes that may occur. Further information will be gained from the effect of radical traps such as Oj or NO, and of various energy transfer agents. 

Hug and Surbeck 35) have proposed the use of Ada. = daL — daR, the difference of the Raman differential scattering cross sections in left and right circularly polarized incident light. This is the Raman equivalent of the circular dichroism Ae = el — eR, where s is the decadic molar extinction coefficient and, unlike the measured (but not the theoretical) IR — IL which depends on both sample and instrumental factors, is solely a molecular parameter. They introduced a chirality number q defined by... 

E being the optical density or absorbance, /q and I the intensities at a fixed wavelength (wave number v) of the exciting beam and the beam after passing through the sample, s is the decade molar extinction coefficient, c the polymer concentration, and d the layer thickness. E is determined directly by the... 

Almost no data have been reported on the decadic molar extinction coefficient, moi/ of localized electrons. The difficulty in obtaining such values rests in the fact that the optical absorption is determined by the product of charge carrier yield, Gfj (see Chapter 5) and the decadic molar extinction coefficient, 01- Gfi must be measured independently. Values estimated by Baxendale et al. (1973) are summarized in Table 11. 

Table 11 Decadic Molar Extinction Coefficient of Localized Electrons in n-Hexane and Methylcyclohexane at X = 1000 nm...

It is customary to express the concentration in Eq. 2.30 in the form of molarity (moles per liter) and the optical path in centimeter. Here, e m) is the so-called decadic molar extinction coefficient, depending on the circular frequency of the radiation co, and it is the typical measure of absorption, especially in the UV region of the spectrum. Its commonly used units are liter per mole per centimeter and is related to the absorption cross section... 

The expressions connecting the observable (the decadic molar extinction coefficient) to the microscopic quantities that can be computed can be derived within a semiclassical [42, 67-74] or a quantum electrodynamic [75, 76] approach. 

This expression connects the observed anisotropy of the decadic molar extinction coefficient to the rotatory strength, Ry, the scalar product of the electric dipole and magnetic dipole transition matrix elements. 

Before moving further, we mention here that the decadic molar extinction coefficient, also known as molar absorptivity, is not the only quantity employed by experimentalists to report their measurements of circular dichroism. Two other quantities often employed are the specific ellipticity [ J/] and the molar ellipticity [ ]. The former is given in degrees cm dm g and is related to the absolute ellipticity ij/, usually given in degrees, by the relationship... 

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