Editing Deuterium (section)

== 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.