Absorption Spectrum
Definition and meaning of Absorption Spectrum in chemistry.
An absorption spectrum is the pattern of dark lines or bands produced when a substance absorbs specific wavelengths of electromagnetic radiation passing through it. Each substance absorbs a characteristic set of wavelengths, so its absorption spectrum acts like a fingerprint.
In more detail
The wavelengths a substance absorbs correspond to the energy gaps between its allowed quantum states: a photon is absorbed only when its energy exactly matches a gap. This makes absorption spectra the basis of techniques such as ultraviolet–visible, infrared, and atomic absorption spectroscopy. An absorption spectrum is the complement of an emission spectrum, in which a substance gives out those same wavelengths.
Key facts
| Shows | Wavelengths a substance absorbs |
|---|---|
| Opposite of | Emission spectrum |
| Used for | Identifying substances |
| Field | Spectroscopy |
The dark Fraunhofer lines in the Sun’s spectrum are an absorption spectrum, caused by cooler gases in the Sun’s atmosphere absorbing specific wavelengths.
Frequently asked questions
What causes an absorption spectrum?
Atoms or molecules absorb photons whose energy matches the gap between two of their energy levels, removing those specific wavelengths from the light that passes through.
How is an absorption spectrum different from an emission spectrum?
An absorption spectrum shows wavelengths removed from light passing through a substance, while an emission spectrum shows the wavelengths a substance gives out. They occur at the same characteristic wavelengths.