08269 IUPAC Gold Book - molar decadic absorption coefficient 10.1351/goldbook.08269 08269 current synonym: molar absorption coefficient 1 Decadic absorbance (\(A_{10}\)) divided by path-length (\(l\)) and amount concentration (\(c\)). \(\varepsilon = A_{10}/(cl)\). 'Extinction coefficient' or 'molar absorptivity' have been widely used for the molar absorption coefficient, unfortunately often with values given in ill-defined units. Use of these terms has been discouraged since the 1960s, when international agreement with non-chemical societies reserved the word where the absorption is linearly proportional to the amount of absorber in unit area 'extinction' for diffusion of radiation, i.e., the sum of the effects of absorption, scattering and luminescence. linear Napierian absorption coefficient https://goldbook.iupac.org//terms/view/08265 molar Napierian absorption coefficient https://goldbook.iupac.org//terms/view/08270 PAC, 2021, 93, 647. 'Glossary of methods and terms used in analytical spectroscopy (IUPAC Recommendations 2019)' on page 667 (https://doi.org/10.1515/pac-2019-0203) https://goldbook.iupac.org/terms/view/08269/html https://goldbook.iupac.org/terms/view/08269/json https://goldbook.iupac.org/terms/view/08269/plain Citation: 'molar decadic absorption coefficient' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.08269 The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using. 2026-05-30T13:16:19+00:00