Molar Absorptivity
The absorbance of a one molar solution measured over a one centimetre path length.
Formula / equation
ε = A / (c l)
Unit
L/(mol·cm)
In depth
Also called the molar extinction coefficient, it is a constant of the substance at a given wavelength and measures how strongly it absorbs. Values above about 10,000 indicate fully allowed transitions, while forbidden d–d transitions give values in the tens.
Examples in the real world
The permanganate ion has ε ≈ 2400 at 525 nm; many organic dyes exceed 50,000.