The first heavy → isotope of
→ hydrogen (2H), the
→ nucleus of which consists of one
→ proton and one → neutron.
Like hydrogen, the deuterium atom has one
electron, and therefore has similar chemical properties to hydrogen, forming, e.g.,
→ heavy water (HDO). Deuterium is generated only during
→ Big Bang nucleosynthesis. It is destroyed in stars through the
reaction D + p → 3He + γ (→ deuterium burning).
As there is no net source of deuterium in stars, its abundance has decreased steadily since the
→ Big Bang, and any value measured today must be a lower limit
on the primordial value. However, → fractionation
processes lead to local → deuterium enhancements; see
→ deuterium abundance for more details. Theoretical models
of Big Bang nucleosynthesis predict D/H to be (2.61 ± 0.15) x 10-5
(Steigman et al. 2007, MNRAS 378, 576) and this is closely matched by measurements from
intergalactic Dα line absorption observations toward high-redshift quasars
that give 2.53±0.04 x 10-5 (Cooke et al. 2014, ApJ 781, 31).
From Gk. deutero-, combining form of deuterios "second" + -ium suffix occurring in scientific coinages on a Latin model. Coined in 1933 by U.S. chemist Harold C. Urey (1893-1981).
Fr.: abondance de deutérium
The number of → deuterium (D) atoms with respect to
→ hydrogen (H) in an astrophysical object.
Deuterium is a primordial product of → Big Bang nucleosynthesis.
According to theoretical models, the primordial D/H ratio is estimated to be
(2.61 ± 0.15) x 10-5 (Steigman et al. 2007, MNRAS 378, 576).
Nuclear reactions in stars convert D into
He tending to a lower D/H ratio in the → interstellar medium
over time (→ deuterium burning).
However, chemical and physical → fractionation
processes can produce local → enhancements in the D/H ratio.
For example, low-temperature ion-molecule reactions in
→ molecular cloud cores can enhance
the D/H ratio in icy grains by as much as two orders of magnitude
above that observed in the interstellar medium.
Fr.: combustion du deutérium
The fusion of a deuterium nucleus with a proton which produces the lightest isotope of helium: D + H → 3He + γ. Deuterium burning occurs in stellar cores at a temperature exceeding 106 K. The onset of deuterium burning marks the end of the → protostellar collapse. It is the only → nuclear reaction that occurs in → brown dwarfs. In normal stars, it is the second step in the → proton-proton chain which leads to the formation of 4He, allowing stars to arrive on the → main sequence.
Fr.: enrichissement de deutérium
The → enrichment of deuterium (D) with respect to
→ hydrogen (H) in
→ Solar System molecules
when compared with the D/H ratio in the
→ interstellar → solar nebula.
H-bearing molecules in → comets,
→ planets, and → chondrite
→ meteorites show a systematic D enrichment
relative to the → molecular hydrogen of the solar
nebula. Because there is no nuclear source for D in the Universe,
the observed → isotopic enrichment must have its
origin in chemical reactions having faster reaction rates for D than for H.
In the Solar nebula the → isotopic fractionation
of D between → water and H followed the reversible reaction:
→ deuterium; → enrichment.
deuterium enrichment factor
karvand-e pordâri-ye doteriom
Fr.: facteur d'enrichissement en deutérium
The ratio between the D/H value in → water
and in → molecular hydrogen, as expressed by:
→ deuterium; → enrichment; → factor.
Fr.: fractionnement de deutérium
The difference between the deuterium (D)/hydrogen (H) → abundance → ratio in an object with respect to that representing a standard or mean value for that type of objects. Same as → isotope fractionation of deuterium. In the gas phase chemistry many of the D fractionation reactions produce an excess of D atoms relative to → hydrogen atoms. Deuterium fractionation in → interstellar cloud cores, → protostars, and → Solar System bodies is frequently used to infer important aspects of their physical and chemical histories. For example, the → deuterium enhancement in the Earth's sea water, with respect to the cosmic abundance, has been interpreted as being due to → enrichment by → comet-like → planetesimals colliding with the young Earth.
→ deuterium; → fractionation.