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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).
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 absorption coefficient can, in turn, be written as a product of either a molar absorptivity of the absorber, ε, and the concentration c of absorbing species in the material, or an absorption cross section, σ, and the (number) density N of absorbers. (see Beer Lambert Law link for full derivation)
ε is the molar attenuation coefficient of that material, and; c(z) is the molar concentration of that material at z. If c(z) is uniform along the path, the relation becomes =. The use of the term "molar absorptivity" for molar attenuation coefficient is discouraged. [1]
In the context of ozone shielding of ultraviolet light, absorption cross section is the ability of a molecule to absorb a photon of a particular wavelength and polarization. Analogously, in the context of nuclear engineering, it refers to the probability of a particle (usually a neutron ) being absorbed by a nucleus.
The Molar attenuation coefficient (also called "molar absorptivity"), which is the absorption coefficient divided by molarity (see also Beer–Lambert law) The mass attenuation coefficient (also called "mass extinction coefficient"), which is the absorption coefficient divided by density; The absorption cross section and scattering cross ...
In science, absorptivity may refer to: Molar absorptivity , in chemistry, a measurement of how strongly a chemical species absorbs light at a given wavelength Absorptance , in physics, the fraction of radiation absorbed at a given wavelength
The molar extinction coefficient of Hb has its highest absorption peak at 420 nm and a second peak at 580 nm. Its spectrum then gradually decreases as light wavelength increases. On the other hand, H b O 2 {\displaystyle HbO2} shows its highest absorption peak at 410 nm, and two secondary peaks at 550 nm and 600 nm.