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• Deuterium (symbol D or 2H, also known as heavy hydrogen) is
one of two stable isotopes of hydrogen. The nuleus ofdeuterium,
alled a deuteron, ontains one proton and one neutron, whereas the
far more ommon hydrogen isotope,protium, has no neutron in the
nuleus. Deuterium has a natural abundane in !arth"s oeans of about
one atom in #$2% ofhydrogen. Thus deuterium aounts for
appro&imately %.%'# (or on a mass basis %.%*'2) of all the
naturally ourringhydrogen in the oeans, while the most ommon
isotope (hydrogen+' or protium) aounts for more than .-.
Theabundane of deuterium hanges slightly from one kind of natural
water to another (see ienna /tandard 0ean 1eanater).
• The deuterium isotope"s name is formed from the 3reek
deuteros meaning 4seond4, to denote the two partiles omposing
the nuleus.5'6 Deuterium was disovered and named in '*' by
Harold 7rey, earning him a Nobel 8ri9e in '*$. This wasfollowed by
the disovery of the neutron in '*2, whih made the nulear struture
of deuterium obvious. /oon afterdeuterium"s disovery, 7rey and
others produed samples of 4heavy water4 in whih the deuterium
ontent had been highlyonentrated.
• Deuterium is destroyed in the interiors of stars faster than
it is produed. 1ther natural proesses are thought to produeonly an
insigni:ant amount of deuterium. Nearly all deuterium found in
nature was produed in the ;ig ;ang '*.- billionyears ago, as the
basi or primordial ratio of hydrogen+' (protium) to deuterium
(about 2# atoms of deuterium per millionhydrogen atoms) has its
origin from that time. This is the ratio found in the gas giant
planets, suh as
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Deuteriumis freCuentlyrepresentedbythehemialsymbolD./ineit
isanisotopeofhydrogenwithmassnumber 2, it
isalsorepresentedby2H.78EAallows bothDand2H,although2His
preferred.56 Edistint hemial symbol is
usedforonvenienebeauseoftheisotope"s ommonuseinvarious sienti:
proesses. Elso,its largemass di=erenewithprotium('H) (deuterium
hasamass of2.%'$'%2u, omparedtothemeanhydrogenatomi weight
of'.%%@$@u,andprotium"s mass of'.%%@-2u) onfersnon+negligiblehemial
dissimilarities with protium+ontainingompounds,whereas
theisotopeweight ratioswithinotherhemial elements
arelargelyinsigni:ant inthis regard.
/petrosopy5e dit6nCuantum mehanis theenergylevels ofeletrons
inatoms dependonthereduedmassofthesystemofeletronandnuleus.For t
hehydrogenatom,theroleofreduedmass is most simplyseeninthe;ohr
modeloftheatom,wherethereduedmass appears ina
simplealulationoftheBydbergonstant andBydbergeCuation,but
thereduedmass alsoappearsinthe/hrGdinger eCuation,andtheDira
eCuationforalulatingatomi energylevels.
Thereduedmass ofthesystemintheseeCuations islosetothemass
ofasingleeletron,but di=ers fromit byasmallamount about eCual
totheratioofmass oftheeletrontotheatomi nuleus.For
hydrogen,thisamount is about '-*@?'-*#,or'.%%%$,andfor deuterium it
isevensmaller*#@'?*#@%,or'.%%%2@2. Theenergies ofspetrosopi lines
for deuteriumandlight+hydrogen(hydrogen+')thereforedi=erbytheratios
ofthesetwonumbers, whihis '.%%%2@2. Thewavelengths
ofalldeuteriumspetrosopi lines areshorter thantheorrespondinglines
oflight hydrogen, byafatorof'.%%%2@2. nastronomial observation,this
orresponds toablueDopplershift of%.%%%2@2times thespeedoflight,
or-'.#km?s.5#6
Thedi=erenes
aremuhmorepronounedinvibrationalspetrosopysuhas
infraredspetrosopyandBamanspetrosopy,5@6 andinrotationalspetrasuhas
mirowavespetrosopybeausethereduedmass ofthedeuteriumis
markedlyhigherthanthat ofprotium.
Deuteriumand; ig;angnul eosynthesis5e
dit60ainartile;ig;angnuleosynthesis
Deuterium is thought tohaveplayed animportant roleinset tingthe
numberandrati osofthe elementstha twereformed inthe;i g;ang.Aombi
ningthermodynamis andthehanges broughtabout byosmi
e&pansion,one analulat ethefra tionofprot ons andneutrons
basedonthe temperatureat thepoint that theuniverse ooledenought
oallow formationof nulei. This alulation indiates sevenprotons
foreveryneutron at thebeginningof nuleogenesis, aratiot
hatwouldremain stableevenaft ernuleogenesis was over.This
frationwas infavorof protonsinit ially,primari lybeauset helowermas
s oftheprot onfavoredtheir prodution.Es theuniverse e&panded,it
ooled. Freeneutrons andprotons areless stablethan helium nulei,
andtheprotons andneutrons hadastrong energeti reasontoform
helium+$.However, forminghelium+$ reCuires theintermediat estepo
fformingdeuteri um.
Throughmuhofthefewminutes after
thebigbangduringwhihnuleosynthesis ouldhaveourred,thetemperaturewas
highenoughthatthemeanenergyperpartilewas greater
thanthebindingenergyofweaklybounddeuteriumIthereforeanydeuteriumthatwasformedwas
immediatelydestroyed. Thissituationis knownas
thedeuteriumbottlenek.
Thebottlenekdelayedformationofanyhelium+$untiltheuniversebeameool
enoughtoformdeuterium (ataboutatemperatureeCuivalent to'%%ke).Et
this point, therewas asuddenburstofelement formation(:rst
deuterium, whihimmediatelyfusedtohelium).However,
veryshortlythereafter, attwentyminutes af ter
the;ig;ang,theuniversebeametoooolfor anyfurther
nulearfusionandnuleosynthesis toour. Etthis point, theelemental
abundanes
werenearly:&ed,withtheonlyhangeassomeoftheradioativeproduts
ofbigbangnuleosynthesis (suhastritium)deay.5-6
Thedeuteriumbottlenekintheformationofhelium,together
withthelakofstableways forhelium toombinewithhydrogenor
withitself(therearenostablenuleiwithmass numbers of:veor eight)
meant that insigni:ant arbon,or anyelementsheavier
thanarbon,formedinthe;ig;ang. Theseelements thus
reCuiredformationinstars. Et
thesametime,thefailureofmuhnuleogenesis
duringthe;ig;angensuredthattherewouldbeplentyofhydrogeninthelater
universeavailabletoform long+livedstars,suhas our/un.
Ebundane5edit6Deuteriumo urs intrae amounts naturallyas
deuteriumgas,writ ten2H2or D2,but most naturalou rreneintheu
niverseis bondedwithatypial 'Hatom,agas alledhydrogendeuteride(
HDor 'H2H).56
Thee&isteneofdeuteriumon!arth,elsewhereinthesolarsystem(as
on:rmedbyplanetaryprobes),andinthespetraofstars,is
alsoanimportantdatum inosmology.3ammaradiationfromordinarynulear
fusiondissoiates deuteriumintoprotons
andneutrons,andtherearenoknownnaturalproesses
otherthanthe;ig;angnuleosynthesis,whihmighthaveprodueddeuterium at
anythinglosetotheobservednatural abundaneofdeuterium(deuterium
isproduedbytherarelusterdeay,andoasional
absorptionofnaturallyourringneutrons bylighthydrogen,but
thesearetrivial soures). Thereis thought
tobelittledeuteriumintheinterior ofthe/unandother stars,as at
temperatures therenulear fusionreations
thatonsumedeuteriumhappenmuhfaster thantheproton+protonreationthat
reatesdeuterium. However,deuterium persists intheouter solar
atmosphereat roughlythesameonentrationas in
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Deuterium is freCuently represented by the hemial
symbol D. /ine it is an isotope
of hydrogen with mass number 2, it is also
represented by 2H. 78EA allowsboth D and 2H, although 2H is
preferred.56 E distint hemial symbol is used f or onveniene
beause of the isotope"s ommon use in various sienti: proesses.Elso,
its large mass di=erene with protium ('H) (deuterium has a
mass of 2.%'$'%2 u, ompared to
the mean hydrogen atomi weight of '.%%@$@ u,
and protium"smass of '.%%@-2 u) onfers non+negligible hemial
dissimilarities with protium+ontaining ompounds, whereas the
isotope weight ratios within other hemialelements are largely
insigni:ant in this regard.Spectroscopy5edit6n Cuantum mehanis
the energy levels of eletrons in atoms depend on the redued
mass of the system of eletron and nuleus. For
the hydrogen atom, the roleof redued mass is most simply
seen in the ;ohr model of the atom, where the redued mass
appears in a simple alulation of the Bydberg onstant and
BydbergeCuation, but the redued mass also appears in
the /hrGdinger eCuation, and the Dira
eCuation for alulating atomi energy levels.
The redued mass of the system in these eCuations is lose
to the mass of a single eletron, but di=ers from it by a small
amount about eCual to the ratio of mass ofthe eletron to the atomi
nuleus. For hyd rogen, this amount is about '-*@?'-*#, or '.%%%$,
and for deuterium it is even smaller *#@'?*#@%, or '.%%%2@2.
Theenergies of spetrosopi lines for deuterium and light+hydrogen
(hydrogen+') therefore di=er by the ratios of these two numbers,
whih is '.%%%2 @2. Thewavelengths of all deuterium spetrosopi lines
are shorter than the orresponding lines of light hydrogen, by a
fator of '.%%%2@2. n astronomial observation,this orresponds to a
blue Doppler shift of %.%%%2@2 times the speed of light, or
-'.# km?s.5#6 The di=erenes are muh more pronouned in
vibrational spetrosopy suh as infrared spetrosopy and Baman
spetrosopy,5@6 and in rotational spetra suh asmirowave
spetrosopy beause the redued mass of the deuterium
is markedly higher than that of p rotium.
Deuterium and Big Bang nucleosynthesis5edit6
Main article: Big Bang nucleosynthesisDeuterium
is thought to have played an important role in setting the
number and ratios of the elements that were formed in the ;ig ;ang.
Aombiningthermodynamis and the hanges brought about by osmi
e&pansion, one an alulate the fration of protons and neutrons
based on the temperature at the pointthat the universe ooled enough
to allow formation of nulei. This alulation indiates seven protons
for every neutron at the beginning of nuleogenesis, a ratiothat
would remain stable even after nuleogenesis was over. This fration
was in favor of protons initially, primarily beause the lower mass
of the proton favoredtheir prodution. Es the universe e&panded,
it ooled. Free neutrons and protons are less stable than
helium nulei, and the protons and neutrons had a strongenergeti
reason to form helium+$. However, forming h elium+$ reCuires the
intermediate step of forming deuterium.
Through muh of the few minutes after the big bang during
whih nuleosynthesis ould have ourred, the temperature was high
enough that the mean energyper partile was greater than the binding
energy of weakly bound d euteriumI therefore any deuterium that was
formed was immediately destroyed. This situation isknown as the
deuterium bottleneck . The bottlenek delayed formation of any
helium+$ until the universe beame ool enough to form deuterium (at
about atemperature eCuivalent to '%% ke). Et this point, there was
a sudden burst of element formation (:rst deuterium, whih
immediately fused to helium). However,very shortly thereafter, at
twenty minutes after the ;ig ;ang, the universe beame too ool for
any further nulear fusion and nuleosynthesis to our. Et this
point,the elemental abundanes were nearly :&ed, with the only
hange as some of the radioativeproduts of big bang
nuleosynthesis (suh
as tritium) deay.5-6 Thedeuterium bottlenek in the
formation of helium, together with the lak of stable ways for
helium to ombine with hydrogen o r with itself (there are no
stable nuleiwith mass numbers of :ve or eight) meant that
insigni:ant arbon, or any elements heavier than arbon, formed
in the ;ig ;ang. These elements thus reCuiredformation in
stars. Et the same time, the failure of muh nuleogenesis
during the ;ig ;ang ensured that there would be plenty of hydrogen
in the later universeavailable to form long+lived stars, suh as our
/un.
Abundance5edit6Deuterium ours in trae amounts naturally as
deuterium gas, written 2H2 or D2, but most natural
ourrene in the universe is bonded with a typial 'H atom, a
gas alled hydrogen deuteride (HD or 'H2H).56
The e&istene of deuterium on !arth, elsewhere in
the solar system (as on:rmed by planetary probes), and in the
spetra of stars, is also an important datum
inosmology. 3amma radiation from ordinary nulear fusion
dissoiates deuterium into protons and neutrons, and there are no
known natural proesses other thanthe ;ig ;ang
nuleosynthesis, whih might have produed deuterium at anything
lose to the observed natural abundane of deuterium (deuterium is
produed bythe rare luster deay, and oasional absorption
of naturally ourring neutrons by light hydrogen, but these are
trivial soures). There is thought to be littledeuterium in the
interior of the /un and other stars, as at temperatures
there nulear fusion reations that onsume deuterium
happen muh faster than theproton+proton reation that reates
deuterium. However, deuterium persists in the outer solar
atmosphere at roughly the same onentration as in
