Also contains definition of: molar decadic absorption coefficient

https://doi.org/10.1351/goldbook.M03972

absorbance divided by the absorption pathlength, l, and the amount concentration, c: \[\varepsilon(\lambda) = \frac{1}{c\, l}\, \text{lg}\! \left ( \frac{P_{\lambda}^{0}}{P_{\lambda}}\right ) = \frac{A(\lambda)}{c\, l}\] where P λ 0 and P λ are, respectively, the incident and transmitted spectral radiant power.**Notes: **

*Source: *

PAC, 2007,*79*, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 371 (https://doi.org/10.1351/pac200779030293)

- The term @M03973@ for molar @A00037@ should be avoided.
- In common usage for \(l/\text{cm}\) and \(c/\text{mol dm}^{-3}\) (\(\text{M}\)), \(\varepsilon(\lambda)\) results in \(\text{dm}^{3}\, \text{mol}^{-1}\, \text{cm}^{-1}\) (\(\text{M}^{-1}\ \text{cm}^{-1}\), the most commonly used unit), which equals \(0.1\ \text{m}^{2}\, \text{mol}^{-1}\) (coherent SI units).

PAC, 2007,