View source for Electromagnetic absorption by water

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[[File:Water infrared absorption coefficient.gif|thumb|350px|link=File:Water infrared absorption coefficient large.gif|Absorption spectrum ([[attenuation coefficient]] vs. wavelength) of liquid water (red),{{r|Bertiewww|Bertie96|tpdsciBertie96}} atmospheric [[water vapor]] (green){{r|spectraiaoru|HITRAN|hitraniaoru|spectraiaoru|Aringer02}} and ice (blue line){{r|atmos|Warren84|AringerWarren02}} between 667 nm and 200 μm.{{r|WozniakDera07}} The plot for vapor is a transformation of data ''Synthetic spectrum for gas mixture {{'}}Pure H<sub>2</sub>O{{'}}'' (296K, 1 atm) retrieved from [[HITRAN|Hitran]] on the Web Information System.{{r|hitraniaoru}}]]

[[File:Absorption spectrum of liquid water.png|thumb|350px|Liquid water absorption [[spectrum]] across a wide [[wavelength]] range<sup>[missing source]</sup>]]

The '''absorption of electromagnetic radiation by water''' depends on the [[state of matter|state]] of the water.

The [[Absorption (electromagnetic radiation)|absorption]] in the gas phase occurs in three regions of the spectrum. [[Rotational spectroscopy|Rotational transitions]] are responsible for absorption in the [[microwave]] and [[far-infrared]], vibrational transitions in the [[mid-infrared]] and [[near-infrared]]. Vibrational bands have rotational fine structure.  Electronic transitions occur in the [[vacuum ultraviolet]] regions.

Liquid water has no rotational spectrum but does absorb in the microwave region. Its weak absorption in the [[visible light|visible spectrum]] results in the pale blue [[color of water]].

== Overview ==

The water molecule, in the gaseous state, has three types of transition that can give rise to absorption of electromagnetic radiation:
* Rotational transitions, in which the molecule gains a quantum of rotational energy. Atmospheric water vapour at ambient temperature and pressure gives rise to absorption in the [[far-infrared]] region of the spectrum, from about 200&nbsp;cm<sup>−1</sup> (50 μm) to longer wavelengths towards the [[microwave]] region.
* Vibrational transitions in which a molecule gains a quantum of vibrational energy. The fundamental transitions give rise to absorption in the [[mid-infrared]] in the regions around 1650&nbsp;cm<sup>−1</sup> (μ band, 6 μm) and 3500&nbsp;cm<sup>−1</sup> (so-called X band, 2.9 μm)
*Electronic transitions in which a molecule is promoted to an excited electronic state. The lowest energy transition of this type is in the [[vacuum ultraviolet]] region.

In reality, vibrations of molecules in the gaseous state are accompanied by rotational transitions, giving rise to a [[Rovibrational coupling|vibration-rotation]] spectrum. Furthermore, vibrational [[overtone]]s and combination bands occur in the [[near-infrared]] region. The [[HITRAN]] [[spectroscopy]] database lists more than 37,000 [[spectral line]]s for gaseous H<sub>2</sub><sup>16</sup>O, ranging from the [[microwave]] region to the [[visible spectrum]].{{r|HITRAN|Gordon}}

In liquid water the rotational transitions are effectively quenched, but absorption bands are affected by [[hydrogen bonding]]. In crystalline ice the vibrational spectrum is also affected by hydrogen bonding and there are [[lattice vibration]]s causing absorption in the far-infrared.  Electronic transitions of gaseous molecules will show both vibrational and rotational fine structure.

=== Units ===
Infrared absorption band positions may be given either in [[wavelength]] (usually in [[micrometre|micrometer]]s, μm) or [[wavenumber]] (usually in [[reciprocal centimeter]]s, cm<sup>−1</sup>) scale.

== Rotational spectrum ==
[[File:Atmospheric terahertz transmittance at Mauna Kea (simulated).svg|250px|thumb|right|Part of the pure rotation absorption spectrum of water vapour]]
[[File:Water molecule rotation animation.gif|thumb|left|Rotating water molecule]]
The water molecule is an [[Rotational spectroscopy|asymmetric top]], that is, it has three independent [[moment of inertia|moments of inertia]]. Rotation about the 2-fold [[symmetry axis]] is illustrated at the left. Because of the low symmetry of the molecule, a large number of transitions can be observed in the [[far infrared]] region of the spectrum. Measurements of [[microwave spectroscopy|microwave spectra]] have provided a very precise value for the O−H [[bond length]], 95.84 ± 0.05 [[picometer|pm]] and H−O−H [[Molecular geometry|bond angle]], 104.5 ± 0.3°.<ref name=Banwell>{{cite book |last1=Banwell |first1=Colin N. |last2=McCash |first2=Elaine M. |title=Fundamentals of molecular spectroscopy |edition= 4th |year=1994 |publisher=McGraw-Hill|isbn=978-0-07-707976-5 |page=50 }}</ref>

==Vibrational spectrum==
{{multiple image
| header    = The three fundamental vibrations of the water molecule
| align     = left

| image1    = Symmetrical stretching.gif
| width1    = 168
| caption1  = ν<sub>1</sub>,O-H symmetric stretching<br>3657&nbsp;cm<sup>−1</sup> (2.734&nbsp;μm)

| image2    = Scissoring.gif
| width2    = 168
| caption2  = ν<sub>2</sub>, H-O-H bending<br>1595&nbsp;cm<sup>−1</sup> (6.269&nbsp;μm)

| image3    = Asymmetrical stretching.gif
| width3    = 168
| caption3  = ν<sub>3</sub>, O-H asymmetric stretching<br>3756&nbsp;cm<sup>−1</sup> (2.662&nbsp;μm)
}}

The water molecule has three fundamental [[molecular vibration]]s. The O-H stretching vibrations give rise to absorption bands with [[Rotational–vibrational coupling|band origins]] at 3657&nbsp;cm<sup>−1</sup> (ν<sub>1</sub>, 2.734&nbsp;μm) and 3756&nbsp;cm<sup>−1</sup> (ν<sub>3</sub>, 2.662&nbsp;μm) in the gas phase. The asymmetric stretching vibration, of B<sub>2</sub> symmetry in the [[Molecular symmetry|point group]] C<sub>2v</sub> is a [[molecular vibration|normal vibration]]. The H-O-H bending mode origin is at 1595&nbsp;cm<sup>−1</sup> (ν<sub>2</sub>, 6.269&nbsp;μm). Both symmetric stretching and bending vibrations have A<sub>1</sub> symmetry, but the frequency difference between them is so large that mixing is effectively zero. In the gas phase all three bands show extensive rotational fine structure.<ref name=Nakamoto>{{cite book |last1=Nakamoto |first1=Kazuo |title=Infrared and Raman spectra of inorganic and coordination compounds|edition= 5th |year=1997|publisher= Wiley |isbn= 978-0-47116394-7|page= 170}}</ref> In the [[Near-infrared spectroscopy|Near-infrared spectrum]]
ν<sub>3</sub> has a series of [[Overtone band|overtones]] at wavenumbers somewhat less than n·ν<sub>3</sub>, n=2,3,4,5... Combination bands, such as ν<sub>2</sub> + ν<sub>3</sub> are also easily observed in the near-infrared region.{{r|Jacquemoud2003}}{{r|PopeFry97}} The presence of [[water vapor]] in the atmosphere is important for [[atmospheric chemistry]] especially as the infrared and near infrared spectra are easy to observe. [[Atmospheric radiative transfer codes|Standard (atmospheric optical) codes]] are assigned to absorption bands as follows. 0.718 μm (visible): α, 0.810 μm: μ, 0.935 μm: ρστ, 1.13 μm: φ, 1.38 μm: ψ, 1.88 μm: Ω, 2.68 μm: X. The gaps between the bands define the [[infrared window]] in the Earth's atmosphere.{{r|Duarte95}}

The infrared spectrum of liquid water is dominated by the intense absorption due to the fundamental O-H stretching vibrations. Because of the high intensity, very short path lengths, usually less than 50 μm, are needed to record the spectra of aqueous solutions. There is no rotational fine structure, but the absorption bands are broader than might be expected, because of [[hydrogen bonding]].{{r|Chaplin}} Peak maxima for liquid water are observed at 3450&nbsp;cm<sup>−1</sup> (2.898 μm), 3615&nbsp;cm<sup>−1</sup> (2.766 μm) and 1640&nbsp;cm <sup>−1</sup> (6.097 μm).<ref name=Nakamoto/> Direct measurement of the infrared spectra of aqueous solutions requires that the cuvette windows be made of substances such as [[calcium fluoride]] which are water-insoluble. This difficulty can alternatively be overcome by using an [[attenuated total reflectance]] (ATR) device rather than [[Absorption spectroscopy|transmission]].

In the near-infrared range liquid water has absorption bands around 1950&nbsp;nm (5128&nbsp;cm<sup>−1</sup>), 1450&nbsp;nm (6896&nbsp;cm<sup>−1</sup>), 1200&nbsp;nm (8333&nbsp;cm<sup>−1</sup>) and 970&nbsp;nm, (10300&nbsp;cm<sup>−1</sup>).{{r|Carter1993|Rossel1998}}{{r|Jacquemoud2003}} The regions between these bands can be used in [[near-infrared spectroscopy]] to measure the spectra of aqueous solutions, with the advantage that glass is transparent in this region, so glass cuvettes can be used. The absorption intensity is weaker than for the fundamental vibrations, but this is not important as longer path-length cuvettes can be used. The absorption band at 698&nbsp;nm (14300&nbsp;cm<sup>−1</sup>) is a 3rd overtone (n=4). It tails off onto the [[visible region]] and is responsible for the intrinsic blue [[color of water]]. This can be observed with a standard UV/vis [[Spectrophotometry|spectrophotometer]], using a 10&nbsp;cm path-length. The colour can be seen by eye by looking through a column of water about 10 m in length; the water must be passed through an [[Ultrafiltration|ultrafilter]] to eliminate color due to [[Rayleigh scattering]] which also can make water appear blue.{{r|PopeFry97|KouLabrieChýlek93|tpdsciPope97Kou93}}

The spectrum of ice is similar to that of liquid water, with peak maxima at 3400&nbsp;cm<sup>−1</sup> (2.941 μm), 3220&nbsp;cm<sup>−1</sup> (3.105 μm) and 1620&nbsp;cm<sup>−1</sup> (6.17 μm)<ref name=Nakamoto/>

In both liquid water and ice clusters, low-frequency vibrations occur, which involve the stretching (TS) or bending (TB) of intermolecular hydrogen bonds (O–H•••O). Bands at wavelengths λ = 50-55 μm or 182-200 cm<sup>−1</sup> (44 μm, 227 cm<sup>−1</sup> in ice) have been attributed to TS, intermolecular stretch, and 200 μm or 50 cm<sup>−1</sup> (166 μm, 60 cm<sup>−1</sup> in ice), to TB, intermolecular bend{{r|WozniakDera07}}

==Visible region==
{|class="wikitable"  style="float: right;"
|+Predicted wavelengths of overtones and combination bands of liquid water in the visible region{{r|PopeFry97}}
|-
! ν<sub>1</sub>, ν<sub>3</sub>!! ν<sub>2</sub> !!wavelength /nm
|- align="center"
| 4 || 0 || 742
|-align="center"
| 4 || 1 || 662
|-align="center"
| 5 || 0 || 605
|-align="center"
| 5 || 1 || 550
|-align="center"
| 6 || 0 || 514
|-align="center"
| 6 || 1 || 474
|-align="center"
| 7 || 0 || 449
|-align="center"
| 7 || 1 || 418
|-align="center"
| 8 || 0 || 401
|-align="center"
| 8 || 1 || 376
|-
|}
[[Attenuation coefficient#Attenuation versus absorption|Absorption coefficients]] for 200&nbsp;nm and 900&nbsp;nm are almost equal at 6.9 m<sup>−1</sup> ([[attenuation length]] of 14.5&nbsp;cm). Very weak light absorption, in the visible region, by liquid water has been measured using an integrating cavity absorption meter (ICAM).{{r|PopeFry97}} The absorption was attributed to a sequence of overtone and combination bands whose intensity decreases at each step, giving rise to an absolute minimum at 418&nbsp;nm, at which wavelength the attenuation coefficient is about 0.0044 m<sup>−1</sup>, which is an attenuation length of about 227 meters. These values correspond to pure absorption without scattering effects. The attenuation of, e.g., a laser beam would be slightly stronger.

[[File:Absorption coefficient of water.svg|thumb|none|350px|Visible light absorption spectrum of pure water ([[attenuation coefficient#Attenuation versus absorption|absorption coefficient]] vs. wavelength){{r|PopeFry97|KouLabrieChýlek93|tpdsciPope97Kou93}}]]

==Electronic spectrum ==
The electronic transitions of the water molecule lie in the [[vacuum ultraviolet]] region. For water vapor the bands have been assigned as follows.{{r|WozniakDera07}}
*65&nbsp;nm band — many different electronic transitions, [[Photoelectrochemical processes#Photoionization|photoionization]], [[photodissociation]]
*discrete features between 115 and 180&nbsp;nm
**set of narrow bands between 115 and 125&nbsp;nm<br />[[Rydberg state|Rydberg series]]: 1''b''<sub>1</sub> (n<sub>2</sub>) → many different Rydberg states and 3''a''<sub>1</sub> (n<sub>1</sub>) → 3''sa''<sub>1</sub> Rydberg state
**128&nbsp;nm band<br />Rydberg series: 3''a''<sub>1</sub> (n<sub>1</sub>) → 3''sa''<sub>1</sub> Rydberg state and 1''b''<sub>1</sub> (n<sub>2</sub>) → 3s''a''<sub>1</sub> Rydberg state
**166.5&nbsp;nm band<br />1''b''<sub>1</sub> (n<sub>2</sub>) → 4''a''<sub>1</sub> (σ<sub>1</sub>*-like [[molecular orbital|orbital]])
:At least some of these transitions result in photodissociation of water into H+OH. Among them the best known is that at 166.5 nm.

==Microwaves and radio waves==
[[File:Dielectric loss water.png|thumb|350px|Dielectric permittivity and dielectric loss of water between 0{{nbsp}}°C and 100{{nbsp}}°C, the arrows showing the effect of increasing temperature<ref>{{cite book |last1=Chaplin |first1=Martin |title= Water Structure and Science|chapter=Water and Microwaves|archive-url=https://web.archive.org/web/20201111221805/http://www1.lsbu.ac.uk/water/microwave_water.html |archive-date=2020-11-11 |chapter-url=http://www1.lsbu.ac.uk/water/microwave_water.html}}</ref>]]
{{See also|Radio window}}

The pure [[Rotational spectroscopy|rotation spectrum]] of water vapor extends into the microwave region.

Liquid water has a broad absorption spectrum in the microwave region, which has been explained in terms of changes in the [[hydrogen bond]] network giving rise to a broad, featureless, microwave spectrum.{{r|Kaatze}} The absorption (equivalent to [[dielectric loss]]) is used in [[microwave oven]]s to heat food that contains water molecules. A frequency of [[ISM band|2.45&nbsp;GHz]], wavelength 122&nbsp;mm, is commonly used.

Radiocommunication at GHz frequencies is very difficult in fresh waters and even more so in salt waters.{{r|WozniakDera07}}

==Atmospheric effects==
{{See also|Infrared window}}
[[File:Synthetic atmosphere absorption spectrum.gif|thumb|350px|Synthetic stick absorption spectrum of a simple gas mixture corresponding to the Earth's atmosphere composition based on [[HITRAN]] data{{r|HITRAN}} created using Hitran on the Web system.{{r|hitraniaoru}} Green color - water vapor, WN – [[wavenumber]] (caution: lower [[wavelength]]s on the right, higher on the left). Water vapor concentration for this gas mixture is 0.4%.]]
Water vapor is a [[greenhouse gas]] in the [[Earth's atmosphere]], responsible for 70% of the known absorption of incoming [[sunlight]], particularly in the infrared region, and about 60% of the atmospheric absorption of [[thermal radiation]] by the Earth known as the [[greenhouse effect]].{{r|Maurellis}} It is also an important factor in [[multispectral imaging]] and [[hyperspectral imaging]] used in [[remote sensing]]{{r|Gordon}} because water vapor absorbs radiation differently in different spectral bands. Its effects are also an important consideration in [[infrared astronomy]] and [[radio astronomy]] in the [[microwave]] or [[millimeter wave]] bands. The [[South Pole Telescope]] was constructed in [[Antarctica]] in part because the elevation and low temperatures there mean there is very little water vapor in the atmosphere.{{r|uchicago}}

Similarly, [[carbon dioxide]] absorption bands occur around 1400, 1600 and 2000&nbsp;nm,{{r|geographyswan}} but its presence in the Earth's atmosphere accounts for just 26% of the greenhouse effect.{{r|Maurellis}} Carbon dioxide gas absorbs energy in some small segments of the thermal infrared spectrum that water vapor misses. This extra absorption within the atmosphere causes the air to warm just a bit more and the warmer the atmosphere the greater its capacity to hold more water vapor. This extra water vapor absorption further enhances the Earth's greenhouse effect.{{r|earthobservatory}}

In the [[Infrared window|atmospheric window]] between approximately 8000 and 14000&nbsp;nm, in the far-infrared spectrum, carbon dioxide and water absorption is weak.{{r|Cotton06}} This window allows most of the thermal radiation in this band to be radiated out to space directly from the Earth's surface. This band is also used for remote sensing of the Earth from space, for example with thermal [[Infrared]] imaging.

As well as absorbing radiation, water vapour occasionally emits radiation in all directions, according to the Black Body Emission curve for its current temperature overlaid on the water absorption spectrum. Much of this energy will be recaptured by other water molecules, but at higher altitudes, radiation sent towards space is less likely to be recaptured, as there is less water available to recapture radiation of water-specific absorbing wavelengths. By the top of the [[troposphere]], about 12&nbsp;km above sea level, most water vapor condenses to liquid water or ice as it releases its [[heat of vapourisation|heat of vapourization]]. Once changed state, liquid water and ice fall away to lower altitudes. This will be balanced by incoming water vapour rising via convection currents.

Liquid water and ice emit radiation at a higher rate than water vapour (see graph above). Water at the top of the troposphere, particularly in liquid and solid states, cools as it emits net photons to space. Neighboring gas molecules other than water (e.g. Nitrogen) are cooled by passing their heat kinetically to the water. This is why temperatures at the top of the troposphere (known as the [[tropopause]]) are about -50 degrees Celsius.

==See also==
* [[Dielectric spectroscopy]]
* [[Differential optical absorption spectroscopy]]
* [[Hydroxyl ion absorption]] in [[optical fiber]]
* [[Water model]]

==References==
{{Reflist|refs=

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<ref name=HITRAN>{{cite web|url=http://www.cfa.harvard.edu/hitran/|title=The HITRAN Database|publisher=Atomic and Molecular Physics Division, Harvard-Smithsonian Center for Astrophysics|access-date=August 8, 2012|quote=HITRAN is a compilation of spectroscopic parameters that a variety of computer codes use to predict and simulate the transmission and emission of light in the atmosphere.}}</ref>

<ref name=Carter1993>{{cite journal|author=Carter, G.A.|author2=McCain, D.C.|year=1993|title=Relationship of leaf spectral reflectance to chloroplast water content determined using NMR microscopy|journal=Remote Sensing of Environment|volume=46|issue=3|pages=305–310|url=http://www.csa.com/partners/viewrecord.php?requester=gs&collection=ENV&recid=3615755|access-date=2007-10-31|quote=Reflectance responses to leaf water content were greatest in the water absorption bands near 1450 nm, 1950 nm, and 2500 nm wavelengths|doi=10.1016/0034-4257(93)90050-8|bibcode=1993RSEnv..46..305C|archive-date=2019-12-13|archive-url=https://web.archive.org/web/20191213014333/http://www.csa.com/partners/viewrecord.php?requester=gs&collection=ENV&recid=3615755|url-status=dead}}</ref>

<ref name=Rossel1998>{{cite journal|author=Rossel, R.A.V.|author2=McBratney, A.B.|year=1998|title=Laboratory evaluation of a proximal sensing technique for simultaneous measurement of soil clay and water content|journal=Geoderma|volume=85|issue=1|pages=19–39|quote=the strong absorption bands of OH groups in soil water at around 1450, 1950 and 2500 nm.|doi=10.1016/S0016-7061(98)00023-8|bibcode=1998Geode..85...19V }}</ref>

<ref name=Jacquemoud2003>{{cite journal|author=Jacquemoud, S.|author2=Ustin, S.L.
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|access-date=2008-10-15|quote=...in the action spectrum of water the three main peaks near 1400, 1950, and 2500 nm, and two minor ones at 970 and 1200 nm}}</ref>

<ref name=Duarte95>{{cite book|editor-last=Duarte|editor-first=F. J.|editor-link=F. J. Duarte|title=Tunable Laser Applications|publisher=M. Dekker|location=New York|year=1995|isbn=978-0-8247-8928-2|quote=There are three sets of water-vapor absorption lines in the near-IR spectral region. Those near 730 and 820 nm are useful for lower tropo- spheric measurements, whereas those near 930 nm are useful for upper- tropospheric measurements...}}</ref>

<ref name=Gordon>{{cite web|url=http://www.cfa.harvard.edu/atmosphere/publications/2007-Diet-JQSRT-XXX.pdf|author=Gordon, Iouli E. |author2=Laurence S. Rothman|author3=Robert R. Gamache|author4=David Jacquemart|author5=Chris Boone|author6=Peter F. Bernathd|author7=Mark W. Shephard|author8=Jennifer S. Delamere|author9=Shepard A. Clough  |title=Current updates of the water-vapor line list in HITRAN: A new ''Diet'' for air-broadened half-widths|access-date=2007-11-03|date=2007-06-24|website=Journal of Quantitative Spectroscopy & Radiative Transfer|quote=Water vapor is the principal absorber of longwave radiation in the terrestrial atmosphere and it has a profound effect on the atmospheric energy budget in many spectral regions. The HITRAN database lists more than 64,000 significant transitions of water vapor ranging from the microwave region to the visible, with intensities that cover many orders of magnitude. These transitions are used, or have to be accounted for, in various remote-sensing applications.}}</ref>

<ref name="WozniakDera07">{{cite book|author1=Wozniak B.|author2=Dera J.|year=2007|title=Atmospheric and Oceanographic Sciences Library|publisher=Springer Science+Business Media. LLC|location=New York|url=https://www.springer.com/cda/content/document/cda_downloaddocument/9780387307534-c2.pdf|access-date=August 4, 2012|isbn=978-0-387-30753-4}}</ref>

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<ref name=atmos>{{cite web|url=http://www.atmos.washington.edu/ice_optical_constants/|title=Optical constants of ice from the ultraviolet to the microwave|author=Richard Brandt}}</ref>

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<ref name="Warren84">{{cite journal|author=Warren S. G.|year=1984|title=Optical constants of ice from the ultraviolet to the microwave|journal=Applied Optics|volume=23|issue=8|pages=1206|url=http://www.atmos.washington.edu/~sgw/PAPERS/1984_Icemcx.pdf|access-date=2012-08-08|bibcode=1984ApOpt..23.1206W|doi=10.1364/AO.23.001206|pmid=18204705 }}</ref>

<ref name=Bertiewww>{{cite web|url=https://www.ualberta.ca/~jbertie/JBDownload.HTM#Spectra|title=John Bertie's Download Site - Spectra|author=John Bertie|access-date=August 8, 2012}}</ref>

<ref name="Bertie96">{{cite journal|author1=Bertie J. E.|author2=Lan Z.|year=1996|title=Infrared Intensities of Liquids XX: The Intensity of the OH Stretching Band of Liquid Water Revisited, and the Best Current Values of the Optical Constants of H2O(l) at 25°C between 15,000 and 1 cm<sup>−1</sup> |journal=Applied Spectroscopy|volume=50|issue=8|pages=1047–1057|url=http://www.opticsinfobase.org/as/abstract.cfm?uri=as-50-8-1047|access-date=2012-08-08|bibcode=1996ApSpe..50.1047B|doi=10.1366/0003702963905385 |s2cid=97329854}}</ref>

<ref name=Maurellis>{{cite web|url=https://physicsworld.com/a/the-climatic-effects-of-water-vapour|title=The climatic effects of water vapour - physicsworld.com|access-date=2019-02-18|date=2003-05-01|author=Maurellis, Ahilleas|website=[[Physics World]]|publisher=[[Institute of Physics]]}}</ref>

<ref name=uchicago>{{cite web|url=http://spt.uchicago.edu/public/southpole.html|title=South Pole Telescope: South Pole : Why is the telescope at the South Pole?|access-date=2007-11-03|publisher=[[University of Chicago]]|quote=Quick Answer: Because the South Pole is probably the best place on Earth for this telescope. It is extremely dry, making the atmosphere exceptionally transparent for SPT.|url-status=dead|archive-url=https://web.archive.org/web/20071015144228/http://spt.uchicago.edu/public/southpole.html|archive-date=2007-10-15}}</ref>

<ref name=geographyswan>{{cite web|url=http://geography.swan.ac.uk/personal/prjn/papers/Prietoetal2005.pdf|title=Satellite estimation of surface/atmosphere parameters: a sensitivity study|access-date=2007-10-31|author=Prieto-Blanco, Ana|author2=Peter R. J. North|author3=Nigel Fox|author4=Michael J. Barnsley|quote=...water absorption bands (around 940nm, 1100nm, 1450nm, 1950nm and 2500nm) and carbon dioxide absorption bands (1400nm, 1600nm and 2000nm)...|url-status=dead|archive-url=https://web.archive.org/web/20110726224839/http://geography.swan.ac.uk/personal/prjn/papers/Prietoetal2005.pdf|archive-date=2011-07-26}}</ref>

<ref name=earthobservatory>{{cite web|url=http://earthobservatory.nasa.gov/Study/Iris/|title=EO Study: Does the Earth have an Iris Analog|publisher=[[NASA]]|access-date=2007-11-04|date=2002-06-17}}</ref>

<ref name=Cotton06>{{cite book|last=Cotton|first=William|title=Human Impacts on Weather and Climate|publisher=Cambridge University Press|location=Cambridge|year=2006|isbn=978-0-521-84086-6|quote=Little absorption is evident in the region called the atmospheric window between 8 and 14&nbsp;μm}}</ref>

<ref name="PopeFry97">{{cite journal|author1=Pope R. M.|author2=Fry E. S.|year=1997|title=Absorption spectrum (380–700 nm) of pure water. II. Integrating cavity measurements|journal=Applied Optics|volume=36|issue=33|pages=8710–8723|doi=10.1364/AO.36.008710|bibcode=1997ApOpt..36.8710P|pmid=18264420 |s2cid=11061625 }}</ref>

<ref name="KouLabrieChýlek93">{{cite journal|author1=Kou L.|author2=Labrie D.|author3=Chýlek P.|year=1993|title=Refractive indices of water and ice the 0.65- to 2.5-μm spectral range|journal=Applied Optics|volume=32|issue=19|pages=3531–3540|doi=10.1364/AO.32.003531|pmid=20829977|bibcode=1993ApOpt..32.3531K }}</ref>

<ref name="tpdsciPope97Kou93">Data of Pope RM and Fry 1997 and of Kou L et al. 1993. In: Miroslaw Jonasz , Top. Part. Disp. Sci. 2007 978-0-9780628-0-4</ref>

<ref name="tpdsciBertie96">Data of Bertie JE and Lan 1996. In: Miroslaw Jonasz , Top. Part. Disp. Sci. 2007 978-0-9780628-0-4</ref>

<ref name=Chaplin>{{cite web|url= http://www1.lsbu.ac.uk/water/microwave_water.html|title=Water Absorption Spectrum|author= Chaplin, Martin|date=2007-10-28|archive-url=https://web.archive.org/web/20201111221805/http://www1.lsbu.ac.uk/water/microwave_water.html|access-date=2007-11-04|archive-date=2020-11-11|quote=In the liquid, rotations tend to be restricted by hydrogen bonds, giving the librations. Also, spectral lines are broader causing overlap of many of the absorption peaks. The main stretching band in liquid water is shifted to a lower frequency and the bending frequency increased by hydrogen bonding.}}</ref>

}}

==External links==
{{Commons}}
* [http://www.spectralcalc.com/ High resolution gas-phase absorption simulations]
* [https://web.archive.org/web/20201111221805/http://www1.lsbu.ac.uk/water/microwave_water.html Water absorption spectrum (Martin Chaplin)] (archived version)

{{Water}}

[[Category:Water physics]]
[[Category:Chemical physics]]
[[Category:Absorption spectroscopy]]
[[Category:Electrochemistry]]
[[Category:Electric and magnetic fields in matter]]