Absorption spectroscopy#Absorption spectrum

An absorption line or absorption spectrum of an electromagnetic spectrum, which occurs when wide-band ( white) light irradiated matter and light quanta (photons ) of certain wavelengths or wavelength ranges to be absorbed thereby (resonance absorption). The absorbed photons are missing in the passing light (Fraunhofer lines). Therefore, the spectrum is dark at the wavelengths in question or black in extreme cases.

If the photons are absorbed by stimulating atoms is sharply defined energy amounts and wavelengths, and the dark areas are correspondingly narrow lines. In molecules, however, often many absorbable energy values ​​close together and form the spectrum broader dark areas, called absorption bands. In any case, the observed absorption spectrum is characteristic of the type of material which passes through the radiation. Therefore, the spectroscopy in different wavelength ranges, or ultraviolet or infrared light, an important method for the analysis of substances.

Be free atoms (for example, gas or steam) spectroscopically, the photons are emitted after absorption again, namely uniformly in all spatial directions. If the light is irradiated from one direction only, so you will find in the transmitted light for the type of atom ( chemical element ) typical absorption spectrum as a line spectrum. The light scattered in the other directions light shows the corresponding emission spectrum.

In the spectroscopy of solids, between the absorption and emission nor any relaxation occur in the solid state. A part of the energy of the photons is converted into heat, for example. In this case the absorption and emission spectra are not, as with the free atoms complementary to each other. In " forbidden lines " it is extremely unlikely that absorption can be observed.


Application find absorption spectra in the (environmental) measurement and analysis technology: With the help of an FTIR spectrometer, for example, the composition of a gas mixture ( eg, air) are investigated quantitatively and qualitatively. Based on the characteristic of each gas absorption spectrum ( "like a fingerprint" ), the amount of this gas are determined in the measured gas mixture.

In atomic absorption spectrometry, the absorption spectrum of a sample is generated and measured. In this way, the atomic composition of the sample determined.

A great importance have absorption spectra in astronomy, because you about them can determine the material composition of luminous celestial body (see the example of the solar spectrum on the right) or - can calculate the speed - on the redshift.