Absorption Cross Section
Definition and meaning of Absorption Cross Section in chemistry.
The absorption cross section is a measure of the probability that an atom or molecule will absorb a photon of a particular energy. It has units of area and represents the effective target size a particle presents to incoming radiation.
In more detail
A larger absorption cross section means a substance absorbs light of that wavelength more strongly. The quantity links directly to the absorption coefficient in the Beer–Lambert law and is widely used in spectroscopy and in atmospheric chemistry, where the cross sections of gases such as ozone determine how much sunlight they absorb.
Key facts
| Symbol | σ (sigma) |
|---|---|
| Units | Area (e.g. cm²) |
| Describes | Photon-absorption probability |
| Field | Spectroscopy |
Ozone has a large absorption cross section in the ultraviolet, which is why the ozone layer absorbs so much of the Sun’s harmful UV radiation.
Frequently asked questions
What does a large absorption cross section mean?
It means the atom or molecule is very likely to absorb a photon of that energy, so it absorbs that wavelength of light strongly.