Absorption spectroscopy

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Absorption spectroscopy is spectroscopy which measures the absorption of radiation by its frequency or wavelength

The absorption occurs when energy, i.e., photons, is absorbed from the radiating field. The intensity of the absorption varies as a function of frequency, and this variation is the absorption spectrum.

In chemistry, the technique is used to detect and measure concentrations of a particular metal element within a solution. The scientists atomise the sample (make it turn to individual atoms) and then see what light wavelengths it absorbs. Each type of chemical (element) absorbs a particular wavelength, so scientists can tell which chemicals are in the sample. Every element has a different atomic absorption spectrum because of the different light wavelengths it absorbs.

The first direct detection and chemical analysis of the atmosphere of an planet outside our solar system. Sodium filters the alien star light of HD 209458 as the hot Jupiter planet passes in front. The process and absorption spectrum are illustrated above. Image Credit: A. Feild, STScI and NASA website.