Absorption Spectroscopy

Name:
Absorption Spectroscopy
Detailed information:
An important technique of instrumental analysis involving measurement of the absorption of radiant energy by a substance as a function of the energy incident upon it. Absorption processes occur throughout the electromagnetic spectrum, ranging from the γ region (nuclear resonance absorption or the Mossbauer effect) to the radio region (nuclear magnetic resonance). In practice, they are limited to those processes that are followed by the emission of radiant energy of greater intensity than that which was absorbed. All absorption processes involve absorption of a photon by the substance being analyzed. If it loses the excess energy by emitting a photon of less energy than that absorbed, fluorescence or phosphorescence is said to occur, depending on the lifetime of the excited state. The emitted energy is normally studied. If the source of radiant energy and the absorbing species are in identical energy states (in resonance) the excess energy is often given up by the nondirectional emission of a photon whose energy is identical with that absorbed. Either absorption or emission may be studied, depending upon the chemical and instrumental circumstances. If the emitted energy is studied, the term resonance fluorescence is often used. However, if the absorbing species releases the excess energy in small steps by intermolecular collision or some other process, it is commonly understood that this phenomenon falls within the realm of absorption spectroscopy. The terms absorption spectroscopy, spectrophotometry, and absorptimetry are often used synonymously. Most absorption spectroscopy is done in the ultraviolet, visible, and infrared regions of the electromagnetic spectrum.See Emission Spectroscopy; Infrared Spectroscopy.