A Unit for Molar Absorptivity (Extinction Coefficient) with Theoretical Significance

Using the nomenclature and symbols recommended by the Committee on Nomenclature in Applied Spectroscopy, absorptivity is defined by the equation (1) a = A/bc where A is the absorbance (optical density) for monochromatic radiation, b is the thickness, and c the concentration. Molar absorptivity is arbitrarily defined for thickness measured in centimeters and concentration in moles/liter. Since A is a pure number, molar absorptivity has the units liters/mole cm. There is at present no single name for this combination of units.