Absorption (electromagnetic radiation)

In physics, absorption is the process by which the energy of a photon is taken up by another entity, for example, by an atom whose valence electrons make transition between two electronic energy levels. The photon is destroyed in the process. The absorbed energy may be re-emitted as radiant energy or transformed into heat energy. The absorption of light during wave propagation is often called attenuation.

The absorbance of an object quantifies how much light is absorbed by it. This may be related to other properties of the object through the Beer-Lambert law.

For most substances, the amount of absorption varies with the wavelength of the light, leading to the appearance of colour in pigments that absorb some wavelengths but not others. For example, an object that absorbs blue, green and yellow light will appear red when viewed under white light. More precise measurements at many wavelengths allow the identification of a substance via absorption spectroscopy.

Earth surface

The specific phenomena involving absorption of electromagnetic radiation at the Earth's surface have several important aspects. These phenomena include regulating the temperature of the Earth's crust, surface waters and lower atmosphere. Changes in the earth's crust (e.g. glaciation, deforestation, polar ice melting) will necessarily alter the quantity and wavelength selectivity of electromagnetic absorption at the Earth's surface; correspondingly changes in climate such as global warming may accompany changes in electomagnetic absorption (or its inverse the albedo).

External links

• Spectral Calculator - Fast and accurate online calculation of molecular absorption spectra.
• Molecular Database Browser - Browse the HITRAN and GEISA databases. Plot absorption lines by position or intensity.