Molar absorption coefficient

In chemistry, the molar absorption coefficient or molar attenuation coefficient (ε) is a measurement of how strongly a chemical species absorbs, and thereby attenuates, light at a given wavelength. It is an intrinsic property of the species. The SI unit of molar absorption coefficient is the square metre per mole (m²/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 m²/mol). In older literature, the cm²/mol is sometimes used; 1 M⁻¹⋅cm⁻¹ equals 1000 cm²/mol. The molar absorption coefficient is also known as the molar extinction coefficient and molar absorptivity, but the use of these alternative terms has been discouraged by the IUPAC.