Editing Infrared spectroscopy (section)

{{Short description|Measurement of infrared radiation's interaction with matter}}
{{For|a table of IR spectroscopy data|infrared spectroscopy correlation table}}
[[File:Osiris-Rex Ovirs gsfc 20150619 2015-12655 019-023.jpg|thumb|OVIRS instrument of the OSIRIS-REx probe is a visible and infrared spectrometer]]
'''Infrared spectroscopy''' ('''IR spectroscopy''' or '''vibrational spectroscopy''') is the measurement of the interaction of [[infrared]] radiation with [[matter]] by [[absorption spectroscopy|absorption]], [[emission spectrum|emission]], or [[reflection (physics)|reflection]]. It is used to study and identify [[chemical substance]]s or [[functional group]]s in solid, liquid, or gaseous forms. It can be used to characterize new materials or identify and verify known and unknown samples. The method or technique of infrared spectroscopy is conducted with an instrument called an '''infrared spectrometer''' (or spectrophotometer) which produces an '''infrared spectrum'''. An IR spectrum can be visualized in a graph of infrared light [[absorbance]] (or [[transmittance]]) on the vertical axis vs. [[frequency]], [[wavenumber]] or [[wavelength]] on the horizontal axis. Typical [[Units of measurement|unit]]s of wavenumber used in IR spectra are [[reciprocal centimeters]], with the symbol cm<sup>−1</sup>. Units of IR wavelength are commonly given in [[micrometre|micrometer]]s (formerly called "microns"), symbol μm, which are related to the wavenumber in a [[Multiplicative inverse|reciprocal]] way. A common laboratory instrument that uses this technique is a [[Fourier transform infrared spectroscopy|Fourier transform infrared]] (FTIR) [[spectrometer]]. Two-dimensional IR is also possible as discussed [[#Two-dimensional IR|below]].

The infrared portion of the [[electromagnetic spectrum]] is usually divided into three regions; the [[Near-infrared spectroscopy|near-]], mid- and [[far infrared|far-]] infrared, named for their relation to the visible spectrum. The higher-energy near-IR, approximately 14,000–4,000&nbsp;cm<sup>−1</sup> (0.7–2.5&nbsp;μm wavelength) can excite [[Overtone band|overtone]] or combination modes of [[molecular vibration]]s. The mid-infrared, approximately 4,000–400&nbsp;cm<sup>−1</sup> (2.5–25&nbsp;μm) is generally used to study the fundamental vibrations and associated [[Rotational–vibrational spectroscopy|rotational–vibrational]] structure. The far-infrared, approximately 400–10&nbsp;cm<sup>−1</sup> (25–1,000&nbsp;μm) has low energy and may be used for [[rotational spectroscopy]] and low frequency vibrations. The region from 2–130&nbsp;cm<sup>−1</sup>, bordering the [[microwave]] region, is considered the [[Terahertz radiation|terahertz]] region and may probe intermolecular vibrations.<ref>{{cite journal | vauthors = Zeitler JA, Taday PF, Newnham DA, Pepper M, Gordon KC, Rades T | title = Terahertz pulsed spectroscopy and imaging in the pharmaceutical setting--a review | journal = The Journal of Pharmacy and Pharmacology | volume = 59 | issue = 2 | pages = 209–23 | date = February 2007 | pmid = 17270075 | doi = 10.1211/jpp.59.2.0008 | s2cid = 34705104 }}</ref> The names and classifications of these subregions are conventions, and are only loosely based on the relative molecular or electromagnetic properties.