Absorption band

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.

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;
• 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;
• the Herzberg bands between 240 and 260 nanometres;
• 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;
• the Huggins bands, weak absorption between 320 and 360 nanometres;
• the Chappius bands, a weak diffuse system between 450 and 650 nanometres in the visible spectrum; and
• the infrared bands centered at 4,700, 9,600 and 14,100 nanometres, the latter being the most intense.