absorptivity [obsolete]

Absorptance divided by the optical path length. For very low attenuance it approximates the absorption coefficient [within the approximation 1 − e − A ∼ A]. The use of this term is not recommended.
Source:
PAC, 1996, 68, 2223 (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2227