Curve of Growth
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Curve of Growth
In spectroscopy, the relationship between the amount of radiant
energy removed by an absorption
line and the number of atoms or molecules of the absorbing gas in the
light path.
If the logarithm of energy absorbed is plotted against the logarithm of
amount of gas in the path, the resulting curve of growth usually has two
straight-line segments. The first, for small absorption and small amounts of
gas, has a slope of 1; the second, for large absorption and large amounts of
gas, has a slope of 1/2. Thus, initially absorption is directly proportional
to the number of atoms or molecules, but as the line becomes more intense,
absorption becomes proportional to the square root of the number of atoms or
molecules. Between these two straight-line segments there is often a portion
in which an increase in the amount of gas in the path produces very little
increase in total absorption. All of this discussion applies in the case of
gaseous emission as
well as absorption.
References
This article is based on NASA's Dictionary of Technical Terms for Aerospace Use
