Editing Absorption spectroscopy (section)

{{Short description|Spectroscopic techniques that measure the absorption of radiation}}
[[File:Spectroscopy overview.svg|thumb|400px|An overview of [[electromagnetic radiation]] absorption. This example discusses the general principle using [[visible spectrum|visible light]]. A white beam [[light source|source]] – emitting light of multiple [[wavelength]]s – is focused on a sample (the [[complementary color]] pairs are indicated by the yellow dotted lines). Upon striking the sample, [[photon]]s that match the energy gap of the [[molecule]]s present (green light in this example) are ''absorbed'' in order to excite the molecule. Other photons transmit unaffected and, if the radiation is in the visible region (400–700 nm), the sample color is the complementary color of the absorbed light. By comparing the [[attenuation]] of the transmitted light with the incident, an absorption spectrum can be obtained.|alt=]]
[[File:Sodium in atmosphere of exoplanet HD 209458.jpg|thumb|400px|The first direct detection and chemical analysis of the [[atmosphere]] of an [[exoplanet]], in 2001. [[Sodium]] in the atmosphere filters the [[starlight]] of [[HD 209458]] as the [[giant planet]] passes in front of the star.]]

'''Absorption spectroscopy''' is [[spectroscopy]] that involves techniques that measure the [[absorption (electromagnetic radiation)|absorption]] of [[electromagnetic radiation]], as a function of [[frequency]] or [[wavelength]], due to its interaction with a sample. The sample absorbs energy, i.e., photons, from the radiating field. The intensity of the absorption varies as a function of frequency, and this variation is the [[#Absorption spectrum|absorption spectrum]]. Absorption spectroscopy is performed across the [[electromagnetic spectrum]].

Absorption spectroscopy is employed as an [[analytical chemistry]] tool to determine the presence of a particular substance in a sample and, in many cases, to quantify the amount of the substance present. [[Infrared spectroscopy|Infrared]] and [[ultraviolet–visible spectroscopy]] are particularly common in analytical applications. Absorption spectroscopy is also employed in studies of molecular and atomic physics, astronomical spectroscopy and remote sensing.

There is a wide range of experimental approaches for measuring absorption spectra. The most common arrangement is to direct a generated beam of radiation at a sample and detect the intensity of the radiation that passes through it. The transmitted energy can be used to calculate the absorption. The source, sample arrangement and detection technique vary significantly depending on the frequency range and the purpose of the experiment.

Following are the major types of absorption spectroscopy:<ref>{{cite book |title=Fundamentals and Techniques of Biophysics and Molecular biology |last=Kumar |first=Pranav |publisher=Pathfinder publication |year=2018 |isbn=978-93-80473-15-4 |location=New Delhi |page=33}}</ref>
{| class="wikitable"
|+
!Sr. No
!Electromagnetic radiation
!Spectroscopic type
|-
|1
|X-ray
|[[X-ray absorption spectroscopy]]
|-
|2
|Ultraviolet–visible
|UV–vis absorption spectroscopy
|-
|3
|Infrared
|IR absorption spectroscopy
|-
|4
|Microwave
|Microwave absorption spectroscopy
|-
|5
|Radio wave
|[[Electron spin resonance spectroscopy]]
[[Nuclear magnetic resonance spectroscopy]]
|}