Editing Deuterium

{{Short description|Isotope of hydrogen with one neutron}}
{{Use dmy dates|date=August 2021}}
{{Infobox isotope
 |image           = Deuterium discharge tube.jpg
 |image_caption   = Deuterium glowing in a gas discharge tube
 |name            = Deuterium, hydrogen-2, D
 |alternate_names = hydrogen-2, D, {{sup|2}}H
 |mass_number     = 2
 |symbol          = H
 |num_neutrons    = 1
 |num_protons     = 1
 |abundance       = 0.0156% (Earth)<ref>{{cite journal |last1=Hagemann |first1=R |last2=Nief |first2=G |last3=Roth |first3=E |name-list-style=vanc |year=1970 |title=Absolute isotopic scale for deuterium analysis of natural waters. Absolute D/H ratio for SMOW&nbsp;1 |journal=[[Tellus A|Tellus]] |volume=22 |issue=6 |pages=712–715 |doi=10.1111/j.2153-3490.1970.tb00540.x|bibcode=1970Tell...22..712H }}</ref>
 |mass            = 2.01410177811{{AME2016 II|ref}}
 |spin            = 1<sup>+</sup>
 |excess_energy   = {{val|13135.720|0.001}}
 |binding_energy  = {{val|2224.57|0.20}}
|halflife=stable}}

'''Deuterium''' ('''hydrogen-2''', symbol '''{{sup|2}}H''' or '''D''', also known as '''heavy hydrogen''') is one of two [[Stable isotope ratio|stable isotopes]] of [[hydrogen]]; the other is protium, or hydrogen-1, {{sup|1}}H. The deuterium [[atomic nucleus|nucleus]] ('''deuteron''') contains one [[proton]] and one [[neutron]], whereas the far more common {{sup|1}}H has no neutrons. 

The name ''deuterium'' comes from Greek ''[[Wikt:δεύτερος|deuteros]]'', meaning "second".<ref>{{cite journal | title = A Name and Symbol for H{{sup|2}} | author1 = [[Harold Urey]] | author2= G. M. Murphy | author3 = [[Ferdinand Brickwedde|F. G. Brickwedde]] | year = 1933 | journal = Journal of Chemical Physics | doi = 10.1063/1.1749326 | volume =1 | issue = 7 | pages = 512–513}}</ref><ref name="diplogen">{{Cite journal | vauthors = O'Leary D | date = February 2012 | title = The deeds to deuterium | journal = Nature Chemistry | volume = 4 | issue = 3 | page = 236 | pmid = 22354440 | doi = 10.1038/nchem.1273 | bibcode = 2012NatCh...4..236O | doi-access = free }}</ref> American chemist [[Harold Urey]] discovered deuterium in 1931. Urey and others produced samples of [[heavy water]] in which the {{sup|2}}H had been highly concentrated. The discovery of deuterium won Urey a [[List of Nobel laureates in Chemistry|Nobel Prize]] in 1934.

Nearly all deuterium found in nature was [[Big Bang nucleosynthesis|synthesized in]] the [[Big Bang]] 13.8&nbsp;billion years ago, forming the primordial ratio of {{sup|2}}H to {{sup|1}}H (≈26&nbsp;deuterium nuclei per 10{{sup|6}} hydrogen nuclei). Deuterium is subsequently produced by the slow stellar [[proton–proton chain]], but rapidly destroyed by exothermic [[Nuclear fusion|fusion reactions]]. The [[Deuterium-deuterium fusion|deuterium-deuterium reaction]] has the second-lowest [[Lawson criterion|energy threshold]], and is the most astrophysically accessible, occurring in both [[stars]] and [[brown dwarfs]].

The [[gas giant]] planets display the primordial ratio of deuterium. Comets show an elevated ratio similar to Earth's oceans (156 deuterium nuclei per 10{{sup|6}} hydrogen nuclei). This reinforces theories that much of Earth's ocean water is of cometary origin.<ref name="nature2">{{cite journal | vauthors = Hartogh P, Lis DC, [[Dominique Bockelée-Morvan|Bockelée-Morvan D]], de Val-Borro M, Biver N, Küppers M, Emprechtinger M, Bergin EA, Crovisier J, Rengel M, Moreno R, Szutowicz S, Blake GA | display-authors = 6 | date = October 2011 | title = Ocean-like water in the Jupiter-family comet 103P/Hartley 2 | journal = Nature | volume = 478 | issue = 7368 | pages = 218–220 | pmid = 21976024 | doi = 10.1038/nature10519 | bibcode = 2011Natur.478..218H| s2cid = 3139621 }}</ref><ref name="Hersant">{{cite journal |last1=Hersant |first1=Franck |last2=Gautier |first2=Daniel |last3=Hure |first3=Jean-Marc | name-list-style = vanc |year=2001 |title=A two-dimensional model for the primordial nebula constrained by D/H measurements in the Solar system: Implications for the formation of giant planets |journal=The Astrophysical Journal |volume=554 |issue=1 |pages=391–407 |bibcode=2001ApJ...554..391H |doi=10.1086/321355 |doi-access=free }} — see fig. 7. for a review of D/H ratios in various astronomical objects</ref> The deuterium ratio of comet [[67P/Churyumov–Gerasimenko]], as measured by the ''[[Rosetta (spacecraft)|Rosetta]]'' space probe, is about three times that of Earth water. This figure is the highest yet measured in a comet, thus deuterium ratios continue to be an active topic of research in both astronomy and climatology.<ref name="sciencemag.org">{{cite journal | vauthors = [[Kathrin Altwegg|Altwegg K]], Balsiger H, Bar-Nun A, Berthelier JJ, Bieler A, Bochsler P, Briois C, Calmonte U, Combi M, De Keyser J, Eberhardt P, Fiethe B, Fuselier S, Gasc S, Gombosi TI, Hansen KC, Hässig M, Jäckel A, Kopp E, Korth A, LeRoy L, Mall U, Marty B, Mousis O, Neefs E, Owen T, Rème H, Rubin M, Sémon T, Tzou CY, Waite H, Wurz P | display-authors = 6 | date = January 2015 | title = Cometary science. 67P/Churyumov–Gerasimenko, a Jupiter family comet with a high D/H ratio | journal = [[Science (journal)|Science]] | volume = 347 | issue = 6220 | page = 1261952 | pmid = 25501976 | doi = 10.1126/science.1261952 | url = https://hal.archives-ouvertes.fr/hal-01346024/file/D%3AH_CG_Science.pdf | bibcode = 2015Sci...347A.387A | s2cid = 206563296 }}</ref>

Deuterium is used in most [[nuclear weapon]]s, many [[fusion power]] experiments, and as the most effective [[neutron moderator]], primarily in [[Pressurized heavy-water reactor|heavy water nuclear reactors]]. It is also used as an [[isotopic label]], in [[Hydrogen isotope biogeochemistry|biogeochemistry]], [[Deuterium NMR|NMR spectroscopy]], and [[deuterated drug]]s.

== Differences from common hydrogen (protium) ==
[[File:Hydrogen deuterium glow comparison.png|thumb|Hydrogen (above) and deuterium (below) glowing in gas discharge tubes]]

=== Chemical symbol ===
Deuterium is often represented by the [[chemical symbol]] D. Since it is an isotope of [[hydrogen]] with [[mass number]] 2, it is also represented by {{sup|2}}H. [[International Union of Pure and Applied Chemistry|IUPAC]] allows both D and {{sup|2}}H, though {{sup|2}}H is preferred.<ref>{{cite web |title=Provisional Recommendations |id=§ IR-3.3.2 |website=Nomenclature of Inorganic Chemistry |series=Chemical Nomenclature and Structure Representation Division |publisher=[[IUPAC]] |url=http://www.iupac.org/reports/provisional/abstract04/connelly_310804.html |access-date=2007-10-03 |url-status=dead |archive-url=https://web.archive.org/web/20061027174015/http://www.iupac.org/reports/provisional/abstract04/connelly_310804.html |archive-date=27 October 2006}}</ref> A distinct chemical symbol is used for convenience because of the isotope's common use in various scientific processes. Also, its large mass difference with [[protium]] ({{sup|1}}H) confers non-negligible chemical differences with {{sup|1}}H compounds. Deuterium has a mass of {{val|2.014102|ul=Da}}, about twice the [[mean]] hydrogen [[atomic weight]] of {{val|1.007947|u=Da}}, or twice protium's mass of {{val|1.007825|u=Da}}. The isotope weight ratios within other elements are largely insignificant in this regard.

=== Spectroscopy ===
In [[quantum mechanics]], the energy levels of electrons in atoms depend on the [[reduced mass]] of the system of electron and nucleus. For a [[hydrogen atom]], the role of reduced mass is most simply seen in the [[Bohr model]] of the atom, where the reduced mass appears in a simple calculation of the [[Rydberg constant]] and Rydberg equation, but the reduced mass also appears in the [[Schrödinger equation]], and the [[Dirac equation]] for calculating atomic energy levels.

The reduced mass of the system in these equations is close to the mass of a single electron, but differs from it by a small amount about equal to the ratio of mass of the electron to the nucleus. For {{sup|1}}H, this amount is about {{sfrac|1837|1836}}, or 1.000545, and for {{sup|2}}H it is even smaller: {{sfrac|3671|3670}}, or 1.0002725. The energies of electronic spectra lines for {{sup|2}}H and {{sup|1}}H therefore differ by the ratio of these two numbers, which is 1.000272. The wavelengths of all deuterium spectroscopic lines are shorter than the corresponding lines of light hydrogen, by 0.0272%. In astronomical observation, this corresponds to a blue Doppler shift of 0.0272% of the [[speed of light]], or 81.6&nbsp;km/s.<ref>{{cite journal | vauthors = Hébrard G, Péquignot D, Vidal-Madjar A, Walsh JR, Ferlet R |date=7 February 2000 |title=Detection of deuterium Balmer lines in the Orion Nebula |journal=Astronomy and Astrophysics |volume=354 |page=L79 |arxiv=astro-ph/0002141 |bibcode=2000A&A...354L..79H}}</ref>

The differences are much more pronounced in vibrational spectroscopy such as [[infrared spectroscopy]] and [[Raman spectroscopy]],<ref>{{cite web |title=Water absorption spectrum |date= |website=[[London South Bank University]] (lsbu.ac.uk) |place=London, UK |url=http://www1.lsbu.ac.uk/water/vibrat.html |url-status=dead <!-- tested 2022-12-21 --> |archive-url=https://web.archive.org/web/20170727144128/http://www1.lsbu.ac.uk/water/vibrat.html |archive-date=27 July 2017}}</ref> and in rotational spectra such as [[microwave spectroscopy]] because the [[reduced mass]] of the deuterium is markedly higher than that of protium. In [[nuclear magnetic resonance spectroscopy]], deuterium has a very different [[nuclear magnetic resonance|NMR]] frequency (e.g. 61&nbsp;MHz when protium is at 400&nbsp;MHz) and is much less sensitive. Deuterated solvents are usually used in protium NMR to prevent the solvent from overlapping with the signal, though [[deuterium NMR]] on its own right is also possible.

=== Big Bang nucleosynthesis ===
{{Main|Big Bang nucleosynthesis}}
Synthesis during the formation of the universe is the only significant way naturally occurring deuterium has been created; it is destroyed in [[stellar fusion]]. Deuterium is thought to have played an important role in setting the number and ratios of the elements that were formed in the [[Big Bang]].<ref>{{Cite journal |last=Particle Data Group |last2=Workman |first2=R L |last3=Burkert |first3=V D |last4=Crede |first4=V |last5=Klempt |first5=E |last6=Thoma |first6=U |last7=Tiator |first7=L |last8=Agashe |first8=K |last9=Aielli |first9=G |last10=Allanach |first10=B C |last11=Amsler |first11=C |last12=Antonelli |first12=M |last13=Aschenauer |first13=E C |last14=Asner |first14=D M |last15=Baer |first15=H |date=2022-08-08 |title=Review of Particle Physics |url=https://academic.oup.com/ptep/article/doi/10.1093/ptep/ptac097/6651666 |journal=Progress of Theoretical and Experimental Physics |language=en |volume=2022 |issue=8 |doi=10.1093/ptep/ptac097 |issn=2050-3911|hdl=1854/LU-01HQG4F6CV7P2F3WWNH4RRN8HD |hdl-access=free }}</ref>{{rp|loc=24.2}} Combining [[thermodynamics]] and the changes brought about by cosmic expansion, one can calculate the fraction of [[protons]] and [[neutrons]] based on the temperature at the point that the universe cooled enough to allow formation of [[Atomic nucleus|nuclei]]. This calculation indicates seven protons for every neutron at the beginning of [[nucleogenesis]], a ratio that would remain stable even after nucleogenesis was over. This fraction was in favor of protons initially, primarily because the lower mass of the proton favored their production. As the Universe expanded, it cooled. [[Free neutron]]s and protons are less stable than [[helium]] nuclei, and the protons and neutrons had a strong energetic reason to form [[helium-4]]. However, forming helium-4 requires the intermediate step of forming deuterium.

Through much of the few minutes after the Big Bang during which nucleosynthesis could have occurred, the temperature was high enough that the mean energy per particle was greater than the binding energy of weakly bound deuterium; therefore, any deuterium that was formed was immediately destroyed. This situation is known as the '''deuterium bottleneck'''. The bottleneck delayed formation of any helium-4 until the Universe became cool enough to form deuterium (at about a temperature equivalent to 100&nbsp;[[keV]]). At this point, there was a sudden burst of element formation (first deuterium, which immediately fused into helium). However, very soon thereafter, at twenty minutes after the Big Bang, the Universe became too cool for any further [[nuclear fusion]] or nucleosynthesis. At this point, the elemental abundances were nearly fixed, with the only change as some of the [[radioactive]] products of Big Bang nucleosynthesis (such as [[tritium]]) decay.<ref>{{cite web |last=Weiss |first=Achim |name-list-style=vanc |title=Equilibrium and change: The physics behind Big Bang nucleosynthesis |website=Einstein Online |url=http://www.einstein-online.info/en/spotlights/BBN_phys/index.html |access-date=2007-02-24 |archive-date=8 February 2007 |archive-url=https://web.archive.org/web/20070208212219/http://www.einstein-online.info/en/spotlights/BBN_phys/index.html |url-status=dead }}</ref> The deuterium bottleneck in the formation of helium, together with the lack of stable ways for helium to combine with hydrogen or with itself (no stable nucleus has a mass number of 5 or 8) meant that an insignificant amount of carbon, or any elements heavier than carbon, formed in the Big Bang. These elements thus required formation in stars. At the same time, the failure of much nucleogenesis during the Big Bang ensured that there would be plenty of hydrogen in the later universe available to form long-lived stars, such as the Sun.

=== Abundance ===
[[File:Standard Model Deuterium.svg|thumb|right|Simplified chart of particle content]]Deuterium occurs in trace amounts naturally as deuterium [[gas]] ({{sup|2}}H{{sub|2}} or D{{sub|2}}), but most deuterium in the [[Universe]] is bonded with {{sup|1}}H to form a gas called [[hydrogen deuteride]] (HD or {{sup|1}}H{{sup|2}}H).<ref>{{cite journal |author=IUPAC Commission on Nomenclature of Inorganic Chemistry |title=Names for muonium and hydrogen atoms and their ions |journal=[[Pure and Applied Chemistry]] |year=2001 |volume=73 |issue=2 |pages=377–380 |doi=10.1351/pac200173020377 |s2cid=97138983 |url=http://www.iupac.org/publications/pac/2001/pdf/7302x0377.pdf |url-status=live |archive-url=https://web.archive.org/web/20030425124156/http://www.iupac.org/publications/pac/2001/pdf/7302x0377.pdf |archive-date=2003-04-25}}</ref> Similarly, natural water contains deuterated molecules, almost all as [[semiheavy water]] HDO with only one deuterium.

The existence of deuterium on Earth, elsewhere in the [[Solar System]] (as confirmed by planetary probes), and in the spectra of [[star]]s, is also an important datum in [[physical cosmology|cosmology]]. Gamma radiation from ordinary nuclear fusion dissociates deuterium into protons and neutrons, and there is no known natural process other than [[Big Bang nucleosynthesis]] that might have produced deuterium at anything close to its observed natural abundance. Deuterium is produced by the rare [[cluster decay]], and occasional absorption of naturally occurring neutrons by light hydrogen, but these are trivial sources. There is thought to be little deuterium in the interior of the Sun and other stars, as at these temperatures the [[nuclear fusion reaction]]s that consume deuterium happen much faster than the [[proton–proton reaction]] that creates deuterium. However, deuterium persists in the outer solar atmosphere at roughly the same concentration as in Jupiter, and this has probably been unchanged since the origin of the Solar System. The natural abundance of {{sup|2}}H seems to be a very similar fraction of hydrogen, wherever hydrogen is found, unless there are obvious processes at work that concentrate it.

The existence of deuterium at a low but constant primordial fraction in all hydrogen is another one of the arguments in favor of the [[Big Bang]] over the [[Steady State theory]] of the Universe. The observed ratios of hydrogen to helium to deuterium in the universe are difficult to explain except with a Big Bang model. It is estimated that the abundances of deuterium have not evolved significantly since their production about 13.8 billion years ago.<ref>{{cite web |title=Cosmic Detectives |url=http://www.esa.int/Our_Activities/Space_Science/Cosmic_detectives |publisher=The European Space Agency (ESA) |date=2 April 2013 |access-date=2013-04-15}}</ref> Measurements of [[Milky Way]] galactic deuterium from ultraviolet spectral analysis show a ratio of as much as 23 atoms of deuterium per million hydrogen atoms in undisturbed gas clouds, which is only 15% below the [[WMAP]] estimated primordial ratio of about 27 atoms per million from the Big Bang. This has been interpreted to mean that less deuterium has been destroyed in star formation in the Milky Way galaxy than expected, or perhaps deuterium has been replenished by a large in-fall of primordial hydrogen from outside the galaxy.<ref>{{cite press release |title=FUSE Satellite solves the case of the missing deuterium |publisher=[[NASA]] |url=http://www.nasa.gov/vision/universe/starsgalaxies/fuse_stars.html |access-date=12 September 2013 |archive-date=14 August 2020 |archive-url=https://web.archive.org/web/20200814054630/https://www.nasa.gov/vision/universe/starsgalaxies/fuse_stars.html |url-status=dead }}</ref> In space a few hundred light years from the Sun, deuterium abundance is only 15 atoms per million, but this value is presumably influenced by differential adsorption of deuterium onto carbon dust grains in interstellar space.<ref>{{cite web |title=Graph of deuterium with distance in our galactic neighborhood |series=FUSE Satellite project |publisher=[[Johns Hopkins University]] |place=Baltimore, MD |url=http://fuse.pha.jhu.edu/wpb/sci_d2h_solved.html |archive-url=https://web.archive.org/web/20131205014518/http://fuse.pha.jhu.edu/wpb/sci_d2h_solved.html |archive-date=5 December 2013 }}
: See also
{{cite journal | vauthors =Linsky JL, Draine BT, Moos HW, Jenkins EB, Wood BE, Oliveira C, Blair WP, Friedman SD, Gry C, Knauth D, Kruk JW | display-authors = 6 |year=2006 |title=What is the Total Deuterium Abundance in the Local Galactic Disk? |journal=The Astrophysical Journal |volume=647 |issue=2 |pages=1106–1124 |doi=10.1086/505556 |bibcode=2006ApJ...647.1106L |arxiv=astro-ph/0608308| s2cid = 14461382 }}</ref>

The abundance of deuterium in [[Jupiter]]'s atmosphere has been directly measured by the [[Galileo space probe|''Galileo'' space probe]] as 26 atoms per million hydrogen atoms. ISO-SWS observations find 22 atoms per million hydrogen atoms in Jupiter.<ref>{{Cite journal | vauthors = Lellouch E, Bézard B, Fouchet T, Feuchtgruber H, [[Thérèse Encrenaz|Encrenaz T]], de Graauw T |year=2001 |title=The deuterium abundance in Jupiter and Saturn from ISO-SWS observations |journal=[[Astronomy & Astrophysics]] |volume=670 |issue=2 |pages=610–622 |doi=10.1051/0004-6361:20010259 |doi-access=free |bibcode=2001A&A...370..610L |url=http://www.aanda.org/articles/aa/pdf/2001/17/aa10609.pdf}}</ref> and this abundance is thought to represent close to the primordial Solar System ratio.<ref name="Hersant" /> This is about 17% of the terrestrial ratio of 156 deuterium atoms per million hydrogen atoms.<!--News reports of Hubble measurements of "6 atoms of 2H per 10,000" in Jupiter are wrong; the correct figure is 6 parts 2H per 100,000 by weight, which is 30 parts per million atom-fraction, close to the Galileo result of 26 parts per million, atom-fraction-->

Comets such as [[Comet Hale-Bopp]] and [[Halley's Comet]] have been measured to contain more deuterium (about 200 atoms per million hydrogens), ratios which are enriched with respect to the presumed protosolar nebula ratio, probably due to heating, and which are similar to the ratios found in Earth seawater. The recent measurement of deuterium amounts of 161 atoms per million hydrogen in Comet [[103P/Hartley]] (a former [[Kuiper belt]] object), a ratio almost exactly that in Earth's oceans (155.76 ± 0.1, but in fact from 153 to 156 ppm), emphasizes the theory that Earth's surface water may be largely from comets.<ref name="nature2"/><ref name="Hersant"/> Most recently the {{sup|2}}H{{sup|1}}HR of [[67P/Churyumov–Gerasimenko]] as measured by ''Rosetta'' is about three times that of Earth water.<ref name="sciencemag.org"/> This has caused renewed interest in suggestions that Earth's water may be partly of asteroidal origin.

Deuterium has also been observed to be concentrated over the mean solar abundance in other terrestrial planets, in particular Mars and Venus.<ref>{{Cite journal |last=Hunten |first=Donald M. |name-list-style=vanc |year=1993 |title=Atmospheric evolution of the terrestrial planets |journal=[[Science (journal)|Science]] |volume=259 |issue=5097 |pages=915–920 |doi=10.1126/science.259.5097.915 |jstor=2880608 |bibcode=1993Sci...259..915H |s2cid=178360068 |issn=0036-8075}}</ref>

=== Production ===
{{main|Heavy water#Production}}
{{RefImprove|date=February 2024}}
Deuterium is produced for industrial, scientific and military purposes, by starting with ordinary water—a small fraction of which is naturally occurring [[heavy water]]—and then separating out the heavy water by the [[Girdler sulfide process]], distillation, or other methods.<ref>{{Cite web |title=Heavy water - Energy Education |url=https://energyeducation.ca/encyclopedia/Heavy_water |access-date=2023-02-08 |website=energyeducation.ca |language=en}}</ref>

In theory, deuterium for heavy water could be created in a nuclear reactor, but separation from ordinary water is the cheapest bulk production process.

The world's leading supplier of deuterium was [[Atomic Energy of Canada Limited]] until 1997, when the last heavy water plant was shut down. Canada uses heavy water as a [[neutron moderator]] for the operation of the [[CANDU reactor]] design.

Another major producer of heavy water is India. All but one of India's atomic energy plants are pressurized heavy water plants, which use natural (i.e., not enriched) uranium. India has eight heavy water plants, of which seven are in operation. Six plants, of which five are in operation, are based on D–H exchange in ammonia gas. The other two plants extract deuterium from natural water in a process that uses [[hydrogen sulfide]] gas at high pressure.

While India is self-sufficient in heavy water for its own use, India also exports reactor-grade heavy water.

== Properties ==

=== Data for molecular deuterium ===
Formula: {{chem2|D2}} or {{chem|2|1|H|2}}

* Density: 0.180 kg/m{{sup|3}} at [[Standard temperature and pressure|STP]] (0 °C, 101325 Pa).
* Atomic weight: 2.0141017926 Da.
* Mean abundance in ocean water (from [[Vienna Standard Mean Ocean Water|VSMOW]]) 155.76 ± 0.1 atoms of deuterium per million atoms of all isotopes of hydrogen (about 1 atom of in 6420); that is, about 0.015% of all atoms of hydrogen (any isotope)

Data at about 18 K for {{sup|2}}H{{sub|2}} ([[triple point]]):
* Density:
** Liquid: 162.4 kg/m{{sup|3}}
** Gas: 0.452 kg/m{{sup|3}}
** Liquefied {{sup|2}}H{{sub|2}}O: 1105.2 kg/m{{sup|3}} at [[Standard temperature and pressure|STP]]
* Viscosity: 12.6 [[pascal second|μPa·s]] at 300 K (gas phase)
* Specific heat capacity at constant pressure ''c{{sub|p}}'':
** Solid: 2950 J/(kg·K)
** Gas: 5200 J/(kg·K)

=== Physical properties ===

Compared to hydrogen in its natural composition on Earth, pure deuterium ({{sup|2}}H{{sub|2}}) has a higher [[melting point]] (18.72&nbsp;K vs. 13.99&nbsp;K), a higher [[boiling point]] (23.64 vs. 20.27&nbsp;K), a higher [[Critical point (thermodynamics)|critical temperature]] (38.3 vs. 32.94&nbsp;K) and a higher critical pressure (1.6496 vs. 1.2858&nbsp;MPa).<ref>{{cite web |title=Deuterium, {{sup|2}}H |series=compounds |website=PubChem |publisher=U.S. [[National Institutes of Health]] |url=https://pubchem.ncbi.nlm.nih.gov/compound/deuterium}}</ref>

The physical properties of deuterium compounds can exhibit significant [[kinetic isotope effect]]s and other physical and chemical property differences from the protium analogs. {{sup|2}}H{{sub|2}}O, for example, is more [[viscous]] than normal {{H2O|link=y}}.<ref>{{RubberBible86th}}</ref> There are differences in bond energy and length for compounds of heavy hydrogen isotopes compared to protium, which are larger than the isotopic differences in any other element. Bonds involving deuterium and [[tritium]] are somewhat stronger than the corresponding bonds in protium, and these differences are enough to cause significant changes in biological reactions. Pharmaceutical firms are interested in the fact that {{sup|2}}H is harder to remove from carbon than {{sup|1}}H.<ref>{{cite news |last=Halford |first=Bethany | name-list-style = vanc |date=4 July 2016 |title=The deuterium switcheroo |newspaper=[[Chemical & Engineering News]] |volume=94 |issue=27 |publisher=[[American Chemical Society]] |pages=32–36 | doi = 10.1021/cen-09427-cover}}</ref>

Deuterium can replace {{sup|1}}H in water molecules to form heavy water ({{sup|2}}H{{sub|2}}O), which is about 10.6% denser than normal water (so that ice made from it sinks in normal water). Heavy water is slightly toxic in [[eukaryotic]] animals, with 25% substitution of the body water causing cell division problems and sterility, and 50% substitution causing death by cytotoxic syndrome (bone marrow failure and gastrointestinal lining failure). [[Prokaryotic]] organisms, however, can survive and grow in pure heavy water, though they develop slowly.<ref>{{cite journal | vauthors = Kushner DJ, Baker A, Dunstall TG | date = February 1999 | title = Pharmacological uses and perspectives of heavy water and deuterated compounds | journal = Canadian Journal of Physiology and Pharmacology | volume = 77 | issue = 2 | pages = 79–88 | pmid = 10535697 | doi = 10.1139/cjpp-77-2-79 }}</ref> Despite this toxicity, consumption of heavy water under normal circumstances does not pose a [[heavy water#Toxicity in humans|health threat]] to humans. It is estimated that a {{convert|70|kg|lb|0|abbr=on}} person might drink {{convert|4.8|L|USgal|abbr=out}} of heavy water without serious consequences.<ref>{{Cite book |chapter-url=https://books.google.com/books?id=nQh7iGX1geIC&pg=PA111 |isbn=978-1-4020-1314-0 |pages=111–112 |chapter=Physiological effect of heavy water |editor=Vertes, Attila |year=2003 |publisher=Kluwer |location=Dordrecht |title=Elements and isotopes: formation, transformation, distribution}}</ref> Small doses of heavy water (a few grams in humans, containing an amount of deuterium comparable to that normally present in the body) are routinely used as harmless metabolic tracers in humans and animals.

=== Quantum properties ===
The deuteron has [[quantum spin|spin]] +1 ("[[triplet state]]") and is thus a [[boson]]. The [[nuclear magnetic resonance|NMR]] frequency of deuterium is significantly different from normal hydrogen. [[Infrared spectroscopy]] also easily differentiates many deuterated compounds, due to the large difference in IR absorption frequency seen in the vibration of a chemical bond containing deuterium, versus light hydrogen. The two stable isotopes of hydrogen can also be distinguished by using [[mass spectrometry]].

The triplet deuteron nucleon is barely bound at {{nowrap|1=''E''{{sub|B}} = {{val|2.23|u=MeV}}}}, and none of the higher energy states are bound. The singlet deuteron is a virtual state, with a negative binding energy of {{val|p=~|60|u=keV}}. There is no such stable particle, but this virtual particle transiently exists during neutron–proton inelastic scattering, accounting for the unusually large neutron scattering cross-section of the proton.<ref>{{cite web |title=Neutron–proton scattering |date=Fall 2004 |website=mightylib.mit.edu |type=course notes |id=22.101 |publisher=[[Massachusetts Institute of Technology]] |url=http://mightylib.mit.edu/Course%20Materials/22.101/Fall%202004/Notes/Part3.pdf |url-status=dead <!-- presumed --> |access-date=2011-11-23 |archive-url=https://web.archive.org/web/20110721213924/http://mightylib.mit.edu/Course%20Materials/22.101/Fall%202004/Notes/Part3.pdf |archive-date=2011-07-21}}</ref>

=== Nuclear properties (deuteron) ===

==== Deuteron mass and radius ====
The deuterium nucleus is called a '''deuteron'''. It has a mass of {{physconst|md_Da}} (just over {{val|1.875|u=GeV/c2}}<ref>{{cite web |title=Deuteron mass energy equivalent in MeV |website=Physics.nist.gov |publisher=U.S. [[National Institute of Standards and Technology]] |url=https://physics.nist.gov/cgi-bin/cuu/Value?mdc2mev |access-date=2024-05-30}}</ref>).

The [[charge radius]] of a deuteron is {{physconst|rd|after=.}}

Like the [[Proton#Charge radius|proton radius]], measurements using [[muon]]ic deuterium produce a smaller result: {{val|2.12562|(78)|ul=fm}}.<ref>{{cite journal | vauthors = Pohl R, Nez F, Fernandes LM, Amaro FD, Biraben F, Cardoso JM, Covita DS, Dax A, Dhawan S, Diepold M, Giesen A, Gouvea AL, Graf T, Hänsch TW, Indelicato P, Julien L, Knowles P, Kottmann F, Le Bigot EO, Liu YW, Lopes JA, Ludhova L, Monteiro CM, Mulhauser F, Nebel T, Rabinowitz P, dos Santos JM, Schaller LA, Schuhmann K, Schwob C, Taqqu D, Veloso JF, Antognini A | display-authors = 6 | date = August 2016 | title = Laser spectroscopy of muonic deuterium | journal = [[Science (journal)|Science]] | volume = 353 | issue = 6300 | pages = 669–673 | pmid = 27516595 | doi = 10.1126/science.aaf2468 | hdl-access = free | collaboration = The CREMA Collaboration | bibcode = 2016Sci...353..669P | hdl = 10316/80061 | s2cid = 206647315 }}</ref>

{{see also|Proton radius puzzle}}

==== Spin and energy ====

Deuterium is one of only five stable [[nuclide]]s with an odd number of protons and an odd number of neutrons. ({{sup|2}}H, [[isotopes of lithium|{{sup|6}}Li]], [[isotopes of boron|{{sup|10}}B]], [[isotopes of nitrogen|{{sup|14}}N]], [[isotopes of tantalum|{{sup|180m}}Ta]]; the long-lived radionuclides [[Potassium-40|{{sup|40}}K]], [[isotopes of vanadium|{{sup|50}}V]], [[isotopes of lanthanum|{{sup|138}}La]], [[isotopes of lutetium|{{sup|176}}Lu]] also occur naturally.) Most [[odd–odd nuclei]] are unstable to [[beta decay]], because the decay products are [[even-even nuclei|even–even]], and thus more strongly bound, due to [[Semi-empirical mass formula#Pairing term|nuclear pairing effects]]. Deuterium, however, benefits from having its proton and neutron coupled to a spin-1 state, which gives a stronger nuclear attraction; the corresponding spin-1 state does not exist in the two-neutron or two-proton system, due to the [[Pauli exclusion principle]] which would require one or the other identical particle with the same spin to have some other different quantum number, such as [[angular momentum operator|orbital angular momentum]]. But orbital angular momentum of either particle gives a lower [[binding energy]] for the system, mainly due to increasing distance of the particles in the steep gradient of the nuclear force. In both cases, this causes the [[diproton]] and [[dineutron]] to be [[unstable]].

The proton and neutron in deuterium can be [[Dissociation (chemistry)|dissociated]] through [[neutral current]] interactions with [[neutrino]]s. The [[Cross section (physics)|cross section]] for this interaction is comparatively large, and deuterium was successfully used as a neutrino target in the [[Sudbury Neutrino Observatory]] experiment.

Diatomic deuterium ({{sup|2}}H{{sub|2}}) has ortho and para [[Spin isomers of hydrogen|nuclear spin isomers]] like diatomic hydrogen, but with [[Spin isomers of hydrogen#Deuterium|differences in the number and population of spin states and rotational levels]], which occur because the deuteron is a [[boson]] with nuclear spin equal to one.<ref name=Hollas>{{cite book |last1=Hollas |first1=J. Michael | name-list-style = vanc |title=Modern Spectroscopy |date=1996 |publisher=John Wiley and Sons |isbn=0-471-96523-5 |page=115 |edition=3rd}}</ref>

====Isospin singlet state of the deuteron ====
Due to the similarity in mass and nuclear properties between the proton and neutron, they are sometimes considered as two symmetric types of the same object, a [[nucleon]]. While only the proton has electric charge, this is often negligible due to the weakness of the [[electromagnetic interaction]] relative to the [[strong nuclear interaction]]. The symmetry relating the proton and neutron is known as [[isospin]] and denoted ''I'' (or sometimes ''T'').

Isospin is an [[SU(2)]] symmetry, like ordinary [[Spin (physics)|spin]], so is completely analogous to it. The proton and neutron, each of which have iso[[spin-1/2]], form an isospin doublet (analogous to a [[spin doublet]]), with a "down" state (↓) being a neutron and an "up" state (↑) being a proton.{{Citation needed|date=November 2019}} A pair of nucleons can either be in an antisymmetric state of isospin called [[Singlet state|singlet]], or in a symmetric state called [[Spin triplet|triplet]]. In terms of the "down" state and "up" state, the singlet is
: <math>\frac{1}{\sqrt{2}}\Big( |{\uparrow\downarrow}\rangle - |{\downarrow\uparrow}\rangle\Big).</math>, which can also be written :<math>\frac{1}{\sqrt{2}}\Big( |p n \rangle - |n p \rangle\Big).</math>

This is a nucleus with one proton and one neutron, i.e. a deuterium nucleus. The triplet is
: <math>
\left(
\begin{array}{ll}
|{\uparrow\uparrow}\rangle\\
\frac{1}{\sqrt{2}}( |{\uparrow\downarrow}\rangle + |{\downarrow\uparrow}\rangle )\\
|{\downarrow\downarrow}\rangle
\end{array}
\right)
</math>
and thus consists of three types of nuclei, which are supposed to be symmetric: a deuterium nucleus (actually a highly [[excited state]] of it), a nucleus with two protons, and a nucleus with two neutrons. These states are not stable.

==== Approximated wavefunction of the deuteron ====
The deuteron wavefunction must be antisymmetric if the isospin representation is used (since a proton and a neutron are not identical particles, the wavefunction need not be antisymmetric in general). Apart from their isospin, the two nucleons also have spin and spatial distributions of their wavefunction. The latter is symmetric if the deuteron is symmetric under [[Parity (physics)|parity]] (i.e. has an "even" or "positive" parity), and antisymmetric if the deuteron is antisymmetric under parity (i.e. has an "odd" or "negative" parity). The parity is fully determined by the total orbital angular momentum of the two nucleons: if it is even then the parity is even (positive), and if it is odd then the parity is odd (negative).

The deuteron, being an isospin singlet, is antisymmetric under nucleons exchange due to isospin, and therefore must be symmetric under the double exchange of their spin and location. Therefore, it can be in either of the following two different states:
* Symmetric spin and symmetric under parity. In this case, the exchange of the two nucleons will multiply the deuterium wavefunction by (−1) from isospin exchange, (+1) from spin exchange and (+1) from parity (location exchange), for a total of (−1) as needed for antisymmetry.
* Antisymmetric spin and antisymmetric under parity. In this case, the exchange of the two nucleons will multiply the deuterium wavefunction by (−1) from isospin exchange, (−1) from spin exchange and (−1) from parity (location exchange), again for a total of (−1) as needed for antisymmetry.

In the first case the deuteron is a spin triplet, so that its total spin ''s'' is 1. It also has an even parity and therefore even orbital angular momentum ''l''. The lower its orbital angular momentum, the lower its energy. Therefore, the lowest possible energy state has {{nowrap|''s'' {{=}} 1}}, {{nowrap|''l'' {{=}} 0}}.

In the second case the deuteron is a spin singlet, so that its total spin ''s'' is 0. It also has an odd parity and therefore odd orbital angular momentum ''l''. Therefore, the lowest possible energy state has {{nowrap|''s'' {{=}} 0}}, {{nowrap|''l'' {{=}} 1}}.

Since {{nowrap|''s'' {{=}} 1}} gives a stronger nuclear attraction, the deuterium [[ground state]] is in the {{nowrap|''s'' {{=}} 1}}, {{nowrap|''l'' {{=}} 0}} state.

The same considerations lead to the possible states of an isospin triplet having {{nowrap|''s'' {{=}} 0}}, {{nowrap|''l'' {{=}} even}} or {{nowrap|''s'' {{=}} 1}}, {{nowrap|''l'' {{=}} odd}}. Thus, the state of lowest energy has {{nowrap|''s'' {{=}} 1}}, {{nowrap|''l'' {{=}} 1}}, higher than that of the isospin singlet.

The analysis just given is in fact only approximate, both because isospin is not an exact symmetry, and more importantly because the [[strong nuclear interaction]] between the two nucleons is related to [[angular momentum]] in [[spin–orbit interaction]] that mixes different ''s'' and ''l'' states. That is, ''s'' and ''l'' are not constant in time (they do not [[commutativity|commute]] with the [[Hamiltonian (quantum mechanics)|Hamiltonian]]), and over time a state such as {{nowrap|''s'' {{=}} 1}}, {{nowrap|''l'' {{=}} 0}} may become a state of {{nowrap|''s'' {{=}} 1}}, {{nowrap|''l'' {{=}} 2}}. Parity is still constant in time, so these do not mix with odd ''l'' states (such as {{nowrap|''s'' {{=}} 0}}, {{nowrap|''l'' {{=}} 1}}). Therefore, the [[quantum state]] of the deuterium is a [[Quantum superposition|superposition]] (a linear combination) of the {{nowrap|''s'' {{=}} 1}}, {{nowrap|''l'' {{=}} 0}} state and the {{nowrap|''s'' {{=}} 1}}, {{nowrap|''l'' {{=}} 2}} state, even though the first component is much bigger. Since the [[total angular momentum]] ''j'' is also a good [[quantum number]] (it is a constant in time), both components must have the same ''j'', and therefore {{nowrap|''j'' {{=}} 1}}. This is the total spin of the deuterium nucleus.

To summarize, the deuterium nucleus is antisymmetric in terms of isospin, and has spin 1 and even (+1) parity. The relative angular momentum of its nucleons ''l'' is not well defined, and the deuteron is a superposition of mostly {{nowrap|''l'' {{=}} 0}} with some {{nowrap|''l'' {{=}} 2}}.

==== Magnetic and electric multipoles ====
In order to find theoretically the deuterium [[magnetic dipole moment]] ''μ'', one uses the formula for a [[nuclear magnetic moment]]
: <math>\mu = 
\frac{1}{j+1}\bigl\langle(l,s),j,m_j{=}j \,\bigr|\, \vec{\mu}\cdot \vec{\jmath} \,\bigl|\,(l,s),j,m_j{=}j\bigr\rangle</math>
with
: <math>\vec{\mu} = g^{(l)}\vec{l} + g^{(s)}\vec{s} </math>
''g''{{sup|(''l'')}} and ''g''{{sup|(''s'')}} are [[g-factor (physics)|''g''-factor]]s of the nucleons.

Since the proton and neutron have different values for ''g''{{sup|(''l'')}} and ''g''{{sup|(''s'')}}, one must separate their contributions. Each gets half of the deuterium orbital angular momentum <math>\vec{l}</math> and spin <math>\vec{s}</math>. One arrives at
: <math>\mu = 
\frac{1}{j+1} \Bigl\langle(l,s),j,m_j{=}j \,\Bigr|\left(\frac{1}{2}\vec{l} {g^{(l)}}_p + \frac{1}{2}\vec{s} ({g^{(s)}}_p + {g^{(s)}}_n)\right)\cdot \vec{\jmath} \,\Bigl|\, (l,s),j,m_j{=}j \Bigr\rangle</math>
where subscripts p and n stand for the proton and neutron, and {{nowrap|''g''<sup>(l)</sup><sub>n</sub> {{=}} 0}}.

By using the same identities as [[Nuclear magnetic moment#Calculating the magnetic moment|here]] and using the value {{nowrap|g<sup>(l)</sup><sub>p</sub> {{=}} 1}}, one gets the following result, in units of the [[nuclear magneton]] ''μ''{{sub|N}}
: <math>\mu = 
\frac{1}{4(j+1)}\left[({g^{(s)}}_p + {g^{(s)}}_n)\big(j(j+1) - l(l+1) + s(s+1)\big) + \big(j(j+1) + l(l+1) - s(s+1)\big)\right]</math>

For the {{nowrap|''s'' {{=}} 1}}, {{nowrap|''l'' {{=}} 0}} state ({{nowrap|''j'' {{=}} 1}}), we obtain
: <math>\mu = \frac{1}{2}({g^{(s)}}_p + {g^{(s)}}_n) = 0.879</math>

For the {{nowrap|''s'' {{=}} 1}}, {{nowrap|''l'' {{=}} 2}} state ({{nowrap|''j'' {{=}} 1}}), we obtain
: <math>\mu = -\frac{1}{4}({g^{(s)}}_p + {g^{(s)}}_n) + \frac{3}{4} = 0.310</math>

The measured value of the deuterium [[magnetic dipole moment]], is {{val|0.857|u=''μ''<sub>N</sub>}}, which is 97.5% of the {{val|0.879|u=''μ''<sub>N</sub>}} value obtained by simply adding moments of the proton and neutron. This suggests that the state of the deuterium is indeed to a good approximation {{nowrap|''s'' {{=}} 1}}, {{nowrap|''l'' {{=}} 0}} state, which occurs with both nucleons spinning in the same direction, but their magnetic moments subtracting because of the neutron's negative moment.

But the slightly lower experimental number than that which results from simple addition of proton and (negative) neutron moments shows that deuterium is actually a linear combination of mostly {{nowrap|''s'' {{=}} 1}}, {{nowrap|''l'' {{=}} 0}} state with a slight admixture of {{nowrap|''s'' {{=}} 1}}, {{nowrap|''l'' {{=}} 2}} state.

The [[electric dipole]] is zero [[Nuclear shell model|as usual]].

The measured electric [[quadrupole]] of the deuterium is {{val|0.2859|u=[[elementary charge|e]]·[[femtometer|fm]]{{sup|2}}}}. While the order of magnitude is reasonable, since the deuteron radius is of order of 1 femtometer (see below) and its [[electric charge]] is e, the above model does not suffice for its computation. More specifically, the [[electric quadrupole]] does not get a contribution from the {{nowrap|1=''l'' = 0}} state (which is the dominant one) and does get a contribution from a term mixing the {{nowrap|1=''l'' = 0}} and the {{nowrap|1=''l'' = 2}} states, because the electric quadrupole [[operator (quantum mechanics)|operator]] does not [[Commutative property#Non-commuting operators in quantum mechanics|commute]] with [[angular momentum]].

The latter contribution is dominant in the absence of a pure {{nowrap|''l'' {{=}} 0}} contribution, but cannot be calculated without knowing the exact spatial form of the nucleons [[wavefunction]] inside the deuterium.

Higher magnetic and electric [[multipole moment]]s cannot be calculated by the above model, for similar reasons.

== Applications ==
=== Nuclear reactors ===
[[File:Deuterium Ionized.JPG|thumb|right|Ionized deuterium in a [[fusor]] reactor giving off its characteristic pinkish-red glow]]
Deuterium is used in [[Heavy water reactor|heavy water moderated fission reactors]], usually as liquid {{sup|2}}H{{sub|2}}O, to slow neutrons without the high neutron absorption of ordinary hydrogen.<ref>See [[neutron cross section#Typical cross sections]]</ref> This is a common commercial use for larger amounts of deuterium.

In [[research reactor]]s, liquid {{sup|2}}H{{sub|2}} is used in cold sources to moderate neutrons to very low energies and wavelengths appropriate for [[neutron scattering|scattering experiments]].

Experimentally, deuterium is the most common [[nuclide]] used in [[nuclear fusion|fusion]] reactor designs, especially in combination with [[tritium]], because of the large reaction rate (or [[nuclear cross section]]) and high [[energy]] yield of the deuterium–tritium (DT) reaction. There is an even higher-yield {{sup|2}}H–[[Helium-3|{{sup|3}}He]] fusion reaction, though the [[Fusion energy gain factor|breakeven point]] of {{sup|2}}H–{{sup|3}}He is higher than that of most other fusion reactions; together with the scarcity of {{sup|3}}He, this makes it implausible as a practical power source, at least until DT and deuterium–deuterium (DD) fusion have been performed on a commercial scale. Commercial nuclear fusion is not yet an accomplished technology.

=== NMR spectroscopy ===
{{See also|Proton NMR|Deuterium NMR}}
[[File:Deuterium lamp 1.png|thumb|right|[[Emission spectrum]] of an ultraviolet [[deuterium arc lamp]]]]
Deuterium is most commonly used in hydrogen [[nuclear magnetic resonance spectroscopy]] ([[proton NMR]]) in the following way. NMR ordinarily requires compounds of interest to be analyzed as dissolved in solution. Because of deuterium's nuclear spin properties which differ from the light hydrogen usually present in organic molecules, NMR spectra of hydrogen/protium are highly differentiable from that of deuterium, and in practice deuterium is not "seen" by an NMR instrument tuned for {{sup|1}}H. Deuterated solvents (including heavy water, but also compounds like deuterated [[chloroform]], CDCl{{sub|3}} or C{{sup|2}}HCl{{sub|3}}, are therefore routinely used in NMR spectroscopy, in order to allow only the light-hydrogen spectra of the compound of interest to be measured, without solvent-signal interference.

Nuclear magnetic resonance spectroscopy can also be used to obtain information about the deuteron's environment in isotopically labelled samples ([[deuterium NMR]]). For example, the configuration of hydrocarbon chains in lipid bilayers can be quantified using solid state deuterium NMR with deuterium-labelled lipid molecules.<ref>{{cite journal | vauthors = Seelig J | date = October 1971 | title = On the flexibility of hydrocarbon chains in lipid bilayers | journal = Journal of the American Chemical Society | volume = 93 | issue = 20 | pages = 5017–5022 | pmid = 4332660 | doi = 10.1021/ja00749a006 }}</ref>

Deuterium NMR spectra are especially informative in the solid state because of its relatively small quadrupole moment in comparison with those of bigger quadrupolar nuclei such as chlorine-35, for example.

=== Mass spectrometry ===
Deuterated (i.e. where all or some hydrogen atoms are replaced with deuterium) compounds are often used as [[internal standard]]s in [[mass spectrometry]]. Like other [[Isotopic labeling|isotopically labeled]] species, such standards improve [[accuracy]], while often at a much lower cost than other isotopically labeled standards. Deuterated molecules are usually prepared via [[hydrogen isotope exchange]] reactions.<ref>J. Atzrodt, V. Derdau, W. J. Kerr, M. Reid, Angew. Chem. Int. Ed. 2018, 57, 3022. https://doi.org/10.1002/anie.201708903</ref><ref>Thomas Junk and W. James Catallo. Hydrogen isotope exchange reactions involving C–H (D, T) bonds. Chem. Soc. Rev., 1997, 26, 401–406. DOI: 10.1039/CS9972600401</ref>

=== Tracing ===
{{Further|Deuterated solvent}}
In [[chemistry]], [[biochemistry]] and [[environmental sciences]], deuterium is used as a non-radioactive, [[Hydrogen isotope biogeochemistry|stable isotopic tracer]], for example, in the [[doubly labeled water test]]. In [[chemical reaction]]s and [[metabolic pathway]]s, deuterium behaves somewhat similarly to ordinary hydrogen (with a few chemical differences, as noted). It can be distinguished from normal hydrogen most easily by its mass, using [[mass spectrometry]] or [[infrared spectrometry]]. Deuterium can be detected by [[femtosecond]] [[infrared]] spectroscopy, since the mass difference drastically affects the frequency of molecular vibrations; {{sup|2}}H–carbon bond vibrations are found in spectral regions free of other signals.

Measurements of small variations in the natural abundances of deuterium, along with those of the stable heavy [[oxygen]] isotopes {{sup|17}}O and {{sup|18}}O, are of importance in [[hydrology]], to trace the geographic origin of Earth's waters. The heavy isotopes of hydrogen and oxygen in rainwater ([[meteoric water]]) are enriched as a function of the temperature of the region where the precipitation falls (and thus enrichment is related to latitude). The relative enrichment of the heavy isotopes in rainwater (as referenced to mean ocean water), when plotted against temperature falls predictably along a line called the [[global meteoric water line]] (GMWL). This plot allows samples of precipitation-originated water to be identified along with general information about the climate in which it originated. Evaporative and other processes in bodies of water, and also ground water processes, also differentially alter the ratios of heavy hydrogen and oxygen isotopes in fresh and salt waters, in characteristic and often regionally distinctive ways.<ref>{{cite web |url=http://www.sahra.arizona.edu/programs/isotopes/oxygen.html |title=Oxygen – Isotopes and Hydrology |publisher=SAHRA |access-date=2007-09-10 |url-status=dead |archive-url=https://web.archive.org/web/20070102124117/http://www.sahra.arizona.edu/programs/isotopes/oxygen.html |archive-date=2 January 2007}}</ref> The ratio of concentration of {{sup|2}}H to {{sup|1}}H is usually indicated with a delta as [[δ2H|δ{{sup|2}}H]] and the geographic patterns of these values are plotted in maps termed as isoscapes. Stable isotopes are incorporated into plants and animals and an analysis of the ratios in a migrant bird or insect can help suggest a rough guide to their origins.<ref>{{cite book |title=Isoscapes: Understanding movement, pattern, and process on Earth through isotope mapping |first=Jason B. |last=West | name-list-style = vanc |publisher=Springer |year=2009}}</ref><ref>{{cite journal | vauthors = Hobson KA, Van Wilgenburg SL, Wassenaar LI, Larson K | year = 2012 | title = Linking hydrogen (δ2H) isotopes in feathers and precipitation: Sources of variance and consequences for assignment to isoscapes | journal = PLOS ONE| volume = 7 | issue = 4 | page = e35137 | pmid = 22509393 | pmc = 3324428 | doi = 10.1371/journal.pone.0035137 | bibcode = 2012PLoSO...735137H | doi-access = free }}</ref>

=== Contrast properties ===
[[Neutron scattering]] techniques particularly profit from availability of deuterated samples: The {{sup|1}}H and {{sup|2}}H cross sections are very distinct and different in sign, which allows contrast variation in such experiments. Further, a nuisance problem of normal hydrogen is its large incoherent neutron cross section, which is nil for {{sup|2}}H. The substitution of deuterium for normal hydrogen thus reduces scattering noise.

Hydrogen is an important and major component in all materials of organic chemistry and life science, but it barely interacts with X-rays. As hydrogen atoms (including deuterium) interact strongly with neutrons; neutron scattering techniques, together with a modern deuteration facility,<ref>{{cite web |title=Deuteration |website=nmi3.eu |publisher=Integrated Infrastructure Initiative for Neutron Scattering and Muon Spectroscopy (NMI3) |url=http://nmi3.eu/about-nmi3/joint-research-activities/deuteration.html |url-status=dead |access-date=2012-01-23 |archive-url=https://web.archive.org/web/20190203064721/https://nmi3.eu/about-nmi3/joint-research-activities/deuteration.html |archive-date=3 Feb 2019}}</ref> fills a niche in many studies of macromolecules in biology and many other areas.

=== Nuclear weapons ===
See below. Most stars, including the Sun, generate energy over most of their lives by fusing hydrogen into heavier elements; yet such fusion of light hydrogen (protium) has never been successful in the conditions attainable on Earth. Thus, all artificial fusion, including the hydrogen fusion in hydrogen bombs, requires heavy hydrogen (deuterium, tritium, or both).<ref>{{Cite web |date=2025-03-14 |title=Nuclear weapon - Gun Assembly, Implosion, Boosting {{!}} Britannica |url=https://www.britannica.com/technology/nuclear-weapon/Gun-assembly-implosion-and-boosting#ref275629 |access-date=2025-03-17 |website=www.britannica.com |language=en}}</ref>

=== Drugs ===
{{Main|Deuterated drug}}
A deuterated drug is a [[small molecule]] medicinal product in which one or more of the [[hydrogen]] atoms in the drug molecule have been replaced by deuterium. Because of the [[kinetic isotope effect]], deuterium-containing drugs may have significantly lower rates of [[metabolism]], and hence a longer [[biological half-life|half-life]].<ref name="pmid19295573">{{cite journal | vauthors = Sanderson K | date = March 2009 | title = Big interest in heavy drugs | journal = Nature | volume = 458 | issue = 7236 | page = 269 | pmid = 19295573 | doi = 10.1038/458269a | s2cid = 4343676 }}</ref><ref name="pmid23744136">{{cite journal | vauthors = Katsnelson A | date = June 2013 | title = Heavy drugs draw heavy interest from pharma backers | journal = Nature Medicine | volume = 19 | issue = 6 | page = 656 | pmid = 23744136 | doi = 10.1038/nm0613-656 | s2cid = 29789127 | doi-access = free }}</ref><ref name="pmid24294889">{{cite journal | vauthors = Gant TG | date = May 2014 | title = Using deuterium in drug discovery: Leaving the label in the drug | journal = Journal of Medicinal Chemistry | volume = 57 | issue = 9 | pages = 3595–3611 | pmid = 24294889 | doi = 10.1021/jm4007998 }}</ref> In 2017, [[deutetrabenazine]] became the first deuterated drug to receive FDA approval.<ref name="First deuterated drug approved">{{cite journal | vauthors = Schmidt C | date = June 2017 | title = First deuterated drug approved | journal = Nature Biotechnology | volume = 35 | issue = 6 | pages = 493–494 | pmid = 28591114 | doi = 10.1038/nbt0617-493 | s2cid = 205269152 }}</ref>

=== Reinforced essential nutrients ===
Deuterium can be used to reinforce specific oxidation-vulnerable C–H bonds within essential or conditionally [[essential nutrients]],<ref>{{cite journal | vauthors = Demidov VV | date = September 2007 | title = Heavy isotopes to avert ageing? | journal = Trends in Biotechnology | volume = 25 | issue = 9 | pages = 371–375 | pmid = 17681625 | doi = 10.1016/j.tibtech.2007.07.007 }}</ref> such as certain [[amino acids]], or [[polyunsaturated fatty acid]]s (PUFA), making them more resistant to oxidative damage. [[Deuterated drug|Deuterated]] polyunsaturated [[fatty acid]]s, such as [[linoleic acid]], slow down the chain reaction of [[lipid peroxidation]] that damage living cells.<ref>Halliwell, Barry; Gutteridge, John M.C. (2015). Free Radical Biology and Medicine (5th ed.). Oxford: Clarendon Press. {{ISBN|9780198717485}}.</ref><ref>{{cite journal | vauthors = Hill S, Lamberson CR, Xu L, To R, Tsui HS, Shmanai VV, Bekish AV, Awad AM, Marbois BN, Cantor CR, Porter NA, Clarke CF, Shchepinov MS | display-authors = 6 | date = August 2012 | title = Small amounts of isotope-reinforced polyunsaturated fatty acids suppress lipid autoxidation | journal = Free Radical Biology & Medicine | volume = 53 | issue = 4 | pages = 893–906 | pmid = 22705367 | pmc = 3437768 | doi = 10.1016/j.freeradbiomed.2012.06.004 }}</ref> Deuterated ethyl ester of linoleic acid ([[RT001]]), developed by Retrotope, is in a [[compassionate use trial]] in [[infantile neuroaxonal dystrophy]] and has successfully completed a Phase I/II trial in [[Friedreich's ataxia]].<ref>{{Cite web|url=https://clinicaltrials.gov/ct2/show/NCT02445794|title = A Randomized, Double-blind, Controlled Study to Assess the Safety, Tolerability, and Pharmacokinetics of RT001 in Patients with Friedreich's Ataxia|date = 24 November 2020}}</ref><ref name="First deuterated drug approved"/>

=== Thermostabilization ===
Live vaccines, such as oral [[polio vaccine]], can be stabilized by deuterium, either alone or in combination with other stabilizers such as [[Magnesium chloride|MgCl{{sub|2}}]].<ref>{{cite journal | vauthors = Wu R, Georgescu MM, Delpeyroux F, Guillot S, Balanant J, Simpson K, Crainic R | date = August 1995 | title = Thermostabilization of live virus vaccines by heavy water (D2O) | journal = Vaccine | volume = 13 | issue = 12 | pages = 1058–1063 | pmid = 7491812 | doi = 10.1016/0264-410X(95)00068-C }}</ref>

=== Slowing circadian oscillations ===
Deuterium has been shown to lengthen the period of oscillation of the circadian clock when dosed in rats, hamsters, and [[Gonyaulax]] dinoflagellates.<ref>{{cite journal |last1=Lesauter |first1=Joseph |last2=Silver |first2=Rae | name-list-style = vanc |date= September 1993 |title=Heavy water lengthens the period of free-running rhythms in lesioned hamsters bearing SCN grafts |journal=Physiology & Behavior |volume=54 |issue=3 |pages=599–604 |issn=0031-9384 |doi=10.1016/0031-9384(93)90255-E |pmid=8415956 |s2cid=32466816 |language=en|doi-access=free }}</ref><ref>{{cite journal | vauthors = McDaniel M, Sulzman FM, Hastings JW | date = November 1974 | title = Heavy water slows the Gonyaulax clock: a test of the hypothesis that D2O affects circadian oscillations by diminishing the apparent temperature | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 71 | issue = 11 | pages = 4389–4391 | pmid = 4530989 | pmc = 433889 | doi = 10.1073/pnas.71.11.4389 | doi-access = free | bibcode = 1974PNAS...71.4389M }}</ref><ref name="Interval Timing Is Preserved Despit">{{cite journal | vauthors = Petersen CC, Mistlberger RE | date = August 2017 | title = Interval timing is preserved despite circadian desynchrony in rats: Constant light and heavy water studies | journal = Journal of Biological Rhythms | volume = 32 | issue = 4 | pages = 295–308 | s2cid = 4633617 | pmid = 28651478 | doi = 10.1177/0748730417716231 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Richter CP | date = March 1977 | title = Heavy water as a tool for study of the forces that control length of period of the 24-hour clock of the hamster | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 74 | issue = 3 | pages = 1295–1299 | pmid = 265574 | pmc = 430671 | doi = 10.1073/pnas.74.3.1295 | doi-access = free | bibcode = 1977PNAS...74.1295R }}</ref> In rats, chronic intake of 25% {{sup|2}}H{{sub|2}}O disrupts circadian rhythm by lengthening the circadian period of [[suprachiasmatic nucleus]]-dependent rhythms in the brain's hypothalamus.<ref name="Interval Timing Is Preserved Despit"/> Experiments in hamsters also support the theory that deuterium acts directly on the suprachiasmatic nucleus to lengthen the free-running circadian period.<ref>{{Cite journal |last1=Lesauter |first1=Joseph |last2=Silver |first2=Rae | name-list-style = vanc |date=September 1993 |title=Heavy water lengthens the period of free-running rhythms in lesioned hamsters bearing SCN grafts |journal=Physiology & Behavior |language=en |volume=54 |issue=3 |pages=599–604 |doi=10.1016/0031-9384(93)90255-E |pmid=8415956|s2cid=32466816|doi-access=free }}</ref>

== History ==

=== Suspicion of lighter element isotopes ===
The existence of nonradioactive isotopes of lighter elements had been suspected in studies of neon as early as 1913,{{citation needed|date=August 2024}} and proven by mass spectrometry of light elements in 1920.{{citation needed|date=August 2024}} At that time the neutron had not yet been discovered, and the prevailing theory was that isotopes of an element differ by the existence of additional ''protons'' in the nucleus accompanied by an equal number of ''[[Discovery of the neutron#Problems of the nuclear electrons hypothesis|nuclear electrons]]''. In this theory, the deuterium nucleus with mass two and charge one would contain two protons and one nuclear electron. However, it was expected that the element hydrogen with a measured average atomic mass very close to {{val|1|u=Da}}, the known mass of the proton, always has a nucleus composed of a single proton (a known particle), and could not contain a second proton. Thus, hydrogen was thought to have no heavy isotopes.{{citation needed|date=August 2024}}

=== Deuterium detected ===
<!--Deuterium was predicted in 1926 by [[Walter Russell]], using his "spiral" periodic table{{Citation needed|date=August 2010}}, and independently by [[Charles Janet]] in 1928.<ref>{{cite journal |last =Stewart |first =Philip J. | name-list-style = vanc |year=2009 |title=Charles Janet: Unrecognized genius of the periodic system |journal=Foundations of Chemistry |volume=12 |pages=5–15 |doi=10.1007/s10698-008-9062-5}}</ref>-->
[[File:Urey.jpg|thumb|upright|Harold Urey, deuterium's discoverer]]
It was first detected spectroscopically in late 1931 by [[Harold Urey]], a chemist at [[Columbia University]]. Urey's collaborator, [[Ferdinand Brickwedde]], [[Distillation|distilled]] five [[liter]]s of [[cryogenics|cryogenically produced]] [[liquid hydrogen]] to {{val|1|ul=mL}} of liquid, using the low-temperature physics laboratory that had recently been established at the National Bureau of Standards (now [[National Institute of Standards and Technology]]) in Washington, DC. The technique had previously been used to isolate heavy isotopes of neon. The cryogenic boiloff technique concentrated the fraction of the mass-2 isotope of hydrogen to a degree that made its spectroscopic identification unambiguous.<ref>{{cite magazine |last1=Brickwedde |first1=Ferdinand G. | name-list-style = vanc |year=1982 |title=Harold Urey and the discovery of deuterium |magazine=[[Physics Today]] |volume=35 |page=34 |doi=10.1063/1.2915259 |bibcode=1982PhT....35i..34B |issue=9}}</ref><ref>{{cite journal | vauthors = Urey H, Brickwedde F, Murphy G |year=1932 |title=A hydrogen isotope of mass&nbsp;2 |journal=Physical Review |volume=39 |issue=1 |pages=164–165 |doi=10.1103/PhysRev.39.164 |bibcode=1932PhRv...39..164U|doi-access=free }}</ref>

=== Naming of the isotope and Nobel Prize ===
Urey created the names ''protium'', ''deuterium'', and ''tritium'' in an article published in 1934. The name is based in part on advice from [[Gilbert N. Lewis]] who had proposed the name "deutium". The name comes from Greek ''deuteros'' 'second', and the nucleus was to be called a "deuteron" or "deuton". Isotopes and new elements were traditionally given the name that their discoverer decided. Some British scientists, such as [[Ernest Rutherford]], wanted to call the isotope "diplogen", from Greek ''diploos'' 'double', and the nucleus to be called "diplon".<ref name=diplogen/><ref>{{cite magazine |title=Deuterium v. Diplogen |date=19 February 1934 |department=Science |magazine=[[Time (magazine)|Time]] |url=http://www.time.com/time/magazine/article/0,9171,746988,00.html |url-status=dead |archive-url=https://web.archive.org/web/20090915180442/http://www.time.com/time/magazine/article/0,9171,746988,00.html |archive-date=15 September 2009}}</ref>

The amount inferred for normal abundance of deuterium was so small (only about 1 atom in 6400 hydrogen atoms in seawater [156 parts per million]) that it had not noticeably affected previous measurements of (average) hydrogen atomic mass. This explained why it hadn't been suspected before. Urey was able to concentrate water to show partial enrichment of deuterium. [[Gilbert N. Lewis|Lewis]], Urey's graduate advisor at [[UC Berkeley College of Chemistry|Berkeley]], had prepared and characterized the first samples of pure heavy water in 1933. The discovery of deuterium, coming before the discovery of the [[neutron]] in 1932, was an experimental shock to [[Nuclear physics|theory]]; but when the neutron was reported, making deuterium's existence more explicable, Urey was awarded the [[Nobel Prize in Chemistry]] only three years after the isotope's isolation. Lewis was deeply disappointed by the [[Nobel Committee for Chemistry|Nobel Committee]]'s decision in 1934 and several high-ranking administrators at Berkeley believed this disappointment played a central role in [[Gilbert N. Lewis#Death|his suicide]] a decade later.<ref>Coffey (2008): 221–222.</ref><ref>{{cite web |last1=Helmenstine |first1=Todd |date=22 March 2018 |title=Today in Science History – March 23 – Gilbert Lewis |url=https://sciencenotes.org/today-in-science-history-march-23-gilbert-lewis/ |access-date=6 August 2020 |website=Science Notes and Projects}}</ref><ref name=":5">{{Cite web |last1=DelVecchio |first1=Rick |last2=Writer |first2=Chronicle Staff |date=2006-08-05 |title=WHAT KILLED FAMED CAL CHEMIST? / 20th century pioneer who failed to win a Nobel Prize may have succumbed to a broken heart, one admirer theorizes |url=https://www.sfgate.com/bayarea/article/WHAT-KILLED-FAMED-CAL-CHEMIST-20th-century-2491757.php |access-date=2019-03-09 |website=SFGate}}</ref><ref name=diplogen/>

=== "Heavy water" experiments in World War II ===
{{Main|Heavy water}}
Shortly before the war, [[Hans von Halban]] and [[Lew Kowarski]] moved their research on neutron moderation from France to Britain, smuggling the entire global supply of heavy water (which had been made in Norway) across in twenty-six steel drums.<ref>{{cite web |last=Sherriff |first=Lucy | name-list-style = vanc |date=1 June 2007 |title=Royal Society unearths top secret nuclear research |newspaper=[[The Register]] |publisher=Situation Publishing Ltd. |url=https://www.theregister.co.uk/2007/06/01/royal_soc_secret_physics/ |access-date=2007-06-03}}</ref><ref>{{cite report |title=The battle for heavy water: Three physicists' heroic exploits |date=25 March 2002 |website=CERN Bulletin |publisher=[[European Organization for Nuclear Research]] |url=https://cds.cern.ch/record/45637?ln=en |access-date=2015-11-02}}</ref>

During [[World War II]], [[Nazi Germany]] was known to be conducting experiments using heavy water as moderator for a [[nuclear reactor]] design. Such experiments were a source of concern because they might allow them to produce [[plutonium]] for an [[atomic bomb]]. Ultimately it led to the [[Allies of World War II|Allied]] operation called the "[[Norwegian heavy water sabotage]]", the purpose of which was to destroy the [[Vemork]] deuterium production/enrichment facility in Norway. At the time this was considered important to the potential progress of the war.

After World War II ended, the Allies discovered that Germany was not putting as much serious effort into the program as had been previously thought. The Germans had completed only a small, partly built experimental reactor (which had been hidden away) and had been unable to sustain a chain reaction. By the end of the war, the Germans did not even have a fifth of the amount of heavy water needed to run the reactor,{{clarify|reason=why did they need heavy water to run a reactor?|date=February 2014}} partially due to the Norwegian heavy water sabotage operation. However, even if the Germans had succeeded in getting a reactor operational (as the U.S. did with [[Chicago Pile-1]] in late 1942), they would still have been at least several years away from the development of an [[atomic bomb]]. The engineering process, even with maximal effort and funding, required about two and a half years (from first critical reactor to bomb) in both the U.S. and [[U.S.S.R.]], for example.

=== In thermonuclear weapons ===
{{main|Thermonuclear weapon}}
[[File:Ivy Mike Sausage device.jpg|right|thumb|upright=1.5|The "Sausage" device casing of the [[Ivy Mike]] [[hydrogen bomb|H bomb]], attached to instrumentation and cryogenic equipment. The 20-ft-tall bomb held a cryogenic [[Dewar flask]] with room for 160&nbsp;kg of liquid deuterium.]]

The 62-ton [[Ivy Mike]] device built by the United States and exploded on 1 November 1952, was the first fully successful [[hydrogen bomb]] (thermonuclear bomb). In this context, it was the first bomb in which most of the energy released came from [[nuclear reaction]] stages that followed the primary [[nuclear fission]] stage of the [[atomic bomb]]. The Ivy Mike bomb was a factory-like building, rather than a deliverable weapon. At its center, a very large cylindrical, insulated [[vacuum flask]] or [[cryostat]], held [[cryogenic]] liquid deuterium in a volume of about 1000 [[liter]]s (160 kilograms in mass, if this volume had been completely filled). Then, a conventional atomic bomb (the "primary") at one end of the bomb was used to create the conditions of extreme temperature and pressure that were needed to set off the [[thermonuclear reaction]].

Within a few years, so-called "dry" hydrogen bombs were developed that did not need cryogenic hydrogen. Released information suggests that all [[thermonuclear weapon]]s built since then contain [[chemical compound]]s of deuterium and lithium in their secondary stages. The material that contains the deuterium is mostly [[lithium deuteride]], with the lithium consisting of the isotope [[lithium-6]]. When the lithium-6 is bombarded with fast [[neutron]]s from the atomic bomb, [[tritium]] (hydrogen-3) is produced, and then the deuterium and the tritium quickly engage in [[thermonuclear fusion]], releasing abundant energy, [[helium-4]], and even more free neutrons. "Pure" fusion weapons such as the [[Tsar Bomba]] are believed to be obsolete. In most modern ("boosted") thermonuclear weapons, fusion directly provides only a small fraction of the total energy. Fission of a natural [[uranium-238]] tamper by fast neutrons produced from D–T fusion accounts for a much larger (i.e. boosted) energy release than the fusion reaction itself.

=== Modern research ===
In August 2018, scientists announced the transformation of gaseous deuterium into a [[Metallic hydrogen|liquid metallic form]]. This may help researchers better understand [[gas giant]] planets, such as Jupiter, Saturn and some [[exoplanet]]s, since such planets are thought to contain a lot of liquid metallic hydrogen, which may be responsible for their observed powerful [[magnetic field]]s.<ref name=NYT-20180816>{{cite news |first=Kenneth |last=Chang | name-list-style = vanc |date=16 August 2018 |title=Settling arguments about hydrogen with 168&nbsp;giant lasers |newspaper=[[The New York Times]] |url=https://www.nytimes.com/2018/08/16/science/metallic-hydrogen-lasers.html |archive-url=https://ghostarchive.org/archive/20220101/https://www.nytimes.com/2018/08/16/science/metallic-hydrogen-lasers.html |archive-date=2022-01-01 |url-access=limited |access-date=18 August 2018}}{{cbignore}}</ref><ref name="SCI-20180816">{{cite press release |title=Under pressure, hydrogen offers a reflection of giant planet interiors |publisher=[[Carnegie Institution for Science]] |date=15 August 2018 |url=https://carnegiescience.edu/news/under-pressure-hydrogen-offers-reflection-giant-planet-interiors |access-date=19 August 2018}}</ref>

== Antideuterium ==
<!-- This section is linked from [[Antihydrogen]] -->

An '''antideuteron''' is the [[antimatter]] counterpart of the deuteron, consisting of an [[antiproton]] and an [[antineutron]]. The antideuteron was first produced in 1965 at the [[Proton Synchrotron]] at [[CERN]]<ref>{{cite journal | vauthors = Massam T, Muller T, Righini B, Schneegans M, Zichichi A |year=1965 |title=Experimental observation of antideuteron production |journal=Il Nuovo Cimento |volume=39 |issue=1 |pages=10–14 |doi=10.1007/BF02814251 |bibcode=1965NCimS..39...10M |s2cid=122952224 }}</ref> and the [[Alternating Gradient Synchrotron]] at [[Brookhaven National Laboratory]].<ref>{{cite journal | vauthors = Dorfan DE, Eades J, Lederman LM, Lee W, Ting CC |date=June 1965 |title=Observation of antideuterons |journal=Physical Review Letters |volume=14 |issue=24 |pages=1003–1006 |doi=10.1103/PhysRevLett.14.1003 |bibcode=1965PhRvL..14.1003D}}</ref> A complete atom, with a [[positron]] orbiting the nucleus, would be called ''antideuterium'', but {{as of|2019|lc=y}} antideuterium has not yet been created. The proposed symbol for antideuterium is {{physics particle|anti=yes|D}}, that is, D with an overbar.<ref>{{cite journal | vauthors = Chardonnet P, Orloff J, Salati P |year=1997 |title=The production of anti-matter in our galaxy  |journal=Physics Letters B |volume=409 |issue=1–4 |pages=313–320 |bibcode=1997PhLB..409..313C |doi=10.1016/S0370-2693(97)00870-8 |arxiv=astro-ph/9705110 |s2cid=118919611 }}</ref>

== See also ==
* [[Isotopes of hydrogen]]
* [[Tokamak]]

== References ==
{{reflist|25em}}

== External links ==
{{Wiktionary}}
* {{cite web
 |title=Nuclear Data Center
 |publisher=[[KAERI]]
 |url=http://atom.kaeri.re.kr/
}}
* {{cite web
 |title=Annotated bibliography for deuterium
 |website=ALSOS: The Digital Library for Nuclear Issues
 |publisher=[[Washington and Lee University]]
 |place=Lexington, VA
 |url=http://alsos.wlu.edu/qsearch.aspx?browse=science/Deuterium
 |url-status=dead |access-date=26 November 2019
 |archive-url=http://webarchive.loc.gov/all/20100505004918/http%3A//alsos.wlu.edu/qsearch.aspx?browse%3Dscience/Deuterium
 |archive-date=5 May 2010
}}
* {{cite news
 |magazine=[[New Scientist]]
 |first=Justin |last=Mullins
 |date=27 April 2005
 |title=Desktop nuclear fusion demonstrated
 |url=https://www.newscientist.com/article/dn7315-desktop-nuclear-fusion-demonstrated/
}}
* {{cite news
 |first=Robin |last=Lloyd
 |date=21 August 2006
 |title=Missing gas found in Milky Way
 |website=Space.com
 |url=https://www.space.com/2771-missing-gas-milky.html
}}

{{Isotope sequence
 |element=hydrogen
 |lighter=[[Hydrogen atom|hydrogen-1]]
 |heavier=[[Tritium]]
 |before=—
 |after=Stable
}}
{{Molecules detected in outer space}}

{{Authority control}}

[[Category:Deuterium| ]]
[[Category:Environmental isotopes]]
[[Category:Isotopes of hydrogen]]
[[Category:Neutron moderators]]
[[Category:Nuclear fusion fuels]]
[[Category:Nuclear materials]]
[[Category:Subatomic particles with spin 1]]
[[Category:Medical isotopes]]