The
absorbance of a beam of collimated monochromatic radiation in a homogeneous
isotropic medium is proportional to the absorption path length,
, and to the concentration,
, or — in the gas phase — to the pressure of the absorbing species. The law can be
expressed as:
or
where the proportionality constant,
, is called the molar (decadic)
absorption coefficient. For
in
and
in
or
,
will result in
or
,
which is a commonly used unit. The SI unit of
is
. Note that
spectral radiant power must be used because the Beer–
Lambert law holds only if the spectral bandwidth of the light is narrow compared to spectral
linewidths in the spectrum.
Source:
PAC, 1996, 68, 2223
(Glossary of terms used in photochemistry (IUPAC Recommendations 1996))
on page 2230
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
PAC, 1990, 62, 2167
(Glossary of atmospheric chemistry terms (Recommendations 1990))
on page 2176
Cite as:
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by
A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997).
XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic,
J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8.
https://doi.org/10.1351/goldbook.
