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The SI unit of molar absorption coefficient is the square metre per mole (m 2 /mol), but in practice, quantities are usually expressed in terms of M −1 ⋅cm −1 or L⋅mol −1 ⋅cm −1 (the latter two units are both equal to 0.1 m 2 /mol).
A. R. Forouhi and I. Bloomer deduced dispersion equations for the refractive index, n, and extinction coefficient, k, which were published in 1986 [1] and 1988. [2] The 1986 publication relates to amorphous materials, while the 1988 publication relates to crystalline.
Extinction coefficient refers to several different measures of the absorption of light in a medium: Attenuation coefficient , sometimes called "extinction coefficient" in meteorology or climatology Mass extinction coefficient , how strongly a substance absorbs light at a given wavelength, per mass density
molar absorption coefficient or molar extinction coefficient, also called molar absorptivity, is the attenuation coefficient divided by molarity (and usually multiplied by ln(10), i.e., decadic); see Beer-Lambert law and molar absorptivity for details;
The points where the molar extinction coefficient spectra of and intersect are called isosbestic points. By using two different wavelengths, it is possible to calculate the concentrations of oxyhemoglobin ( C H b O 2 {\displaystyle C_{HbO2}} ) and deoxyhemoglobin ( C H b {\displaystyle C_{Hb}} ) as shown in the following equations:
ε i is the molar attenuation coefficient of the attenuating species i in the material sample; c i is the amount concentration of the attenuating species i in the material sample, by definition of attenuation cross section and molar attenuation coefficient. Attenuation cross section and molar attenuation coefficient are related by
Variable pathlength absorption spectroscopy uses a determined slope to calculate concentration. As stated above this is a product of the molar absorptivity and the concentration. Since the actual absorbance value is taken at many data points at equal intervals, background subtraction is generally unnecessary.
where λ is a wavelength, is the optical path length of the cuvette which contains the solution of the N compounds (chromophores), , is the molar absorbance (also known as the extinction coefficient) of the ith chemical species at the wavelength λ, c i is its concentration. When the concentrations have been calculated as above and absorbance ...