Absorbance Napierian units

Using eq. (1.39), relationships are obtained in the case of Napierian units for the absorption coefficients and the absorbance E at the wavelength of irradiation X. ... 

In formal kinetics the symbols A, B,... are used for the reactants. The symbol E is used to represent absorbance in this book. Napierian units are used in this chapter (see Section 1.4.3). In Chapters 4 and 5 decadic units are used for convenience and the decadic molar absorption coefficient is indicated by B as used in Section 1.4.4. 

Derivations assume that reactant A absorbs the radiation and starts the photoreaction. Napierian units are used. Intense stirring of the solution is required. The Bodenstein hypothesis is valid for all the photophysical intermediates. 

In Chapter 3 Napierian units were used for absorption coefficients and absorbance. The reason was a simpler handling of the equations. Since instrumentation reads decadic units, they are used in most equations in this chapter. The decadic molar spectral absorption coefficient e of the compounds (i) varies with wavelength A. For this reason Bouguer-Lambert-Beer s law is restricted to monochromatic radiation. This restriction and the interactions between molecules in concentrated solutions cause two problems in applying the law to quantitative evaluation ... 

In this and the following example k and E describe the absorption coefficients and the absorbances at the wavelength of irradiation as derived in Chapter 3 (Napierian units). For any wavelength of measurement A one finds according to eqs. (3.56) and (3.62)(since = 0)... 

In eq. (5.155) Napierian units are used, although decadic units are given in the table. Seven cases are given. In each the absorbance at the wavelength of irradiation at the end of the reaction amounts to that at the beginning multiplied by some factor. 

Finally, the molecular absorption cross-section capture area of a molecule. Operationally, it can be calculated as the (Napierian) absorption coefficient divided by the number N of molecular entities contained in a unit volume of the absorbing medium along the light path ... 

The term Bouguer-Lambert law is not familiar to many spectroscopists. The term Beer-Lambert law or merely Beer s law is frequently used in its place. Technically, Beer s law refers to the observation that the contribution of an absorber to the absorbance of a sample is proportional to the concentration of the absorber. The symbol k is referred to by some spectroscopists as the Beer-Lambert absorption coejficient. Because of the possibility of decadic or napierian absorbance and the various units by which concentration can be expressed, several different quantities are all Beer-Lambert absorption coefficients. The term absorptivity is commonly used in equations for decadic absorbance and can include concentration in any rmits. The term linear absorption coefficient is the usual name for the linear napierian absorption coefficient of a pure material. 

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