Title: molar decadic absorption coefficient
Long Title: IUPAC Gold Book - molar decadic absorption coefficient
DOI: 10.1351/goldbook.08269
Status: current

Definition
Decadic absorbance (\(A_{10}\)) divided by path-length (\(l\)) and amount concentration (\(c\)). \(\varepsilon = A_{10}/(cl)\).


Note
'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.

Related Terms
- linear Napierian absorption coefficient: https://goldbook.iupac.org//terms/view/08265
- molar Napierian absorption coefficient: https://goldbook.iupac.org//terms/view/08270

Source
- 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)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/08269/html
- json: https://goldbook.iupac.org/terms/view/08269/json
- xml: https://goldbook.iupac.org/terms/view/08269/xml

Citation: 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
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Accessed: 2026-05-30T13:17:47+00:00