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.
extinction coefficient
Lambert law
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]