https://doi.org/10.1351/goldbook.B00626
The @A00028@ of a beam of collimated monochromatic radiation in a homogeneous @I03353@ medium is proportional to the absorption path length, \(l\), and to the concentration, \(c\), or — in the gas phase — to the pressure of the absorbing species. The law can be expressed as: \[A = \text{log}_{10}\left ( \frac{P_{\lambda }^{0}}{P_{\lambda }} \right ) = \varepsilon \:c\:l\] or \[P_{\lambda }=P_{\lambda }^{0}10^{-\varepsilon \: c\: l}\] where the proportionality constant, \(\varepsilon\), is called the molar (decadic) @A00037@. For \(l\) in \(\text{cm}\) and \(c\) in \(\text{mol dm}^{-3}\) or \(\text{M}\), \(\varepsilon\) will result in \(\text{dm}^{3}\ \text{mol}^{-1}\ \text{cm}^{-1}\) or \(\text{M}^{-1}\ \text{cm}^{-1}\), which is a commonly used unit. The SI unit of \(\varepsilon\) is \(\text{m}^{2}\ \text{mol}^{-1}\). Note that @S05828@ must be used because the Beer–@L03445@ holds only if the spectral bandwidth of the light is narrow compared to spectral linewidths in the spectrum.
See:
absorbance
, extinction coefficient
, Lambert law
Source:
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2230 [Terms] [Paper]
PAC, 1996, 68, 2223. (Glossary of terms used in photochemistry (IUPAC Recommendations 1996)) on page 2230 [Terms] [Paper]
See also:
PAC, 1988, 60, 1449. (Nomenclature, symbols, units and their usage in spectrochemical analysis - VII. Molecular absorption spectroscopy, ultraviolet and visible (UV/VIS) (Recommendations 1988)) on page 1452 [Terms] [Paper]
PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2176 [Terms] [Paper]
PAC, 1988, 60, 1449. (Nomenclature, symbols, units and their usage in spectrochemical analysis - VII. Molecular absorption spectroscopy, ultraviolet and visible (UV/VIS) (Recommendations 1988)) on page 1452 [Terms] [Paper]
PAC, 1990, 62, 2167. (Glossary of atmospheric chemistry terms (Recommendations 1990)) on page 2176 [Terms] [Paper]