Absorption band
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An absorption band is a range of wavelengths (or, equivalently, frequencies) in the electromagnetic spectrum within which electromagnetic energy is absorbed by a substance. See absorption spectrum. Under the right conditions, an absorption band can become an emission band.
When the absorbing substance is a polyatomic gas, an absorption band actually is composed of a group of discrete absorption lines which appear to overlap. Each line is associated with a particular mode of vibration or rotation induced in a gas molecule by the incident radiation.
The absorption bands of oxygen and ozone are often referred to in the literature of atmospheric physics.
The important bands for oxygen are:
- the Hopfield bands, very strong, between about 67 and 100 nanometres in the ultraviolet (named after John J. Hopfield);
- a diffuse system between 101.9 and 130 nanometres;
- the Schumann-Runge continuum, very strong, between 135 and 176 nanometres;
- the Schumann-Runge bands between 176 and 192.6 nanometres (named for Victor Schumann and Carl Runge);
- the Herzberg bands between 240 and 260 nanometres (named after Gerhard Herzberg);
- the atmospheric bands between 538 and 771 nanometres in the visible spectrum; and
- a system in the infrared at about 1000 nanometres.
The important bands for ozone are:
- the Hartley bands between 200 and 300 nanometres in the ultraviolet, with a very intense maximum absorption at 255 nanometres (named after Walter Noel Hartley);
- the Huggins bands, weak absorption between 320 and 360 nanometres (named after Sir William Huggins);
- the Chappuis bands (sometimes misspelled "Chappius"), a weak diffuse system between 375 and 650 nanometres in the visible spectrum (named after J. Chappuis); and
- the Wulf bands in the infrared beyond 700 nm, centered at 4,700, 9,600 and 14,100 nanometres, the latter being the most intense (named after Oliver R. Wulf).
For nitrogen, there is:
- The Lyman-Birge-Hopfield bands, sometimes known as the Birge-Hopfield bands, in the far ultraviolet: 140– 170 nm (named after Theodore Lyman, Raymond T. Birge, and John J. Hopfield)
