Absorption band
An absorption band is a wavelength interval in which the electromagnetic radiation , e.g. B. solar radiation , is selectively absorbed ("sucked up", "swallowed") on the way to the recipient by chemical substances (e.g. atmospheric gases such as carbon dioxide , carbon monoxide , ozone , methane ...) . Certain intervals of the entire wavelength range emitted by the radiation source are no longer available. The originally continuous spectrum of the radiation source arrives at the receiver with dark gaps, the absorption bands. The image of the spectrum obtained is called the band spectrum , more precisely: the absorption spectrum .
An absorption band consists of a large number of individual (singular) absorption lines lying close together . They arise as a result of the coupling of electrical oscillation and rotation excitation in molecules , so that no individual energy difference is absorbed, but an entire spectrum of energy values (the absorption spectrum ), depending on the excitation of the molecules. For certain materials and conditions, the absorption band at the corresponding resolution are split into individual absorption lines, which statements about the vibration / excitation state permits the corresponding substance; one speaks of the fine structure of the absorption band. The different molecules only absorb in a wavelength interval that is specific to them.
application
The absorption bands are of particular importance for meteorology and air chemistry . The earth's atmosphere , the air , is a gas mixture in which substances with the most varied of absorption properties occur. Therefore, the radiation emitted by the sun does not reach the earth's surface completely, but only those wavelength intervals that were not absorbed by the various gas molecules in the air on their way through the atmosphere. The atmosphere is therefore permeable to these wavelength ranges, which is why one speaks here of an atmospheric window .
