The act of linking together or forming couples; a connection between two things so they
move together.
The quality of coupled systems or the way they are coupled.

Cosmology: In the early history of the Universe, separation of matter
and radiation due to their non-interaction. At a redshift of 1000, that is about 400,000
years after the Big Bang, the temperature would have cooled to the point (4000 degrees Kelvin)
where electrons and nuclei can recombine and form neutral hydrogen atoms. Since atoms do not
scatter the radiation appreciably, free electrons were lacking, and the Universe became
transparent to radiation. Same as → recombination.
See also → decoupling era.

Verbal noun of decouple, from → de- +
→ couple + → -ing.

The dimensionless gravitational constant defined as the gravitational
attraction between pair of electrons and normally given by:
α_{G} = (Gm_{e}^{2}) / (ħc)
= (m_{e} / m_{P})^{2}
~ 1.7518 × 10^{-45}, where ħ is
→ Planck's reduced constant,
c the → speed of light,
m_{e}
is the → electron mass, and
m_{P} is the → Planck mass.

A coupling scheme of electronic → spin angular momenta
and → orbital angular momenta
for heavy atoms (generally Z > 30), where the spin and orbital
angular momenta of individual electrons couple strongly, and
therefore the → LS coupling scheme does not apply.
The coupling between spin and orbital angular momentum of each electron is much
stronger than the coupling between different electrons. Therefore,
the total angular momentum,
j_{i}, for the i-th electron is obtained by combining
l_{i} and s_{i} and then coupling these
j's together to give
the total angular momentum J = Σ_{i} j_{i}.
In the jj coupling scheme the total orbital angular momentum quantum
number, L, and the total spin angular momentum number, S,
are not specified.

j referring to the symbol of the total angular momentum for individual
electrons; → coupling.

A coupling scheme of → electron configuration,
used mainly for the lighter atoms with → atomic number
less than 30.
In an atom when changes in energy states are produced by the action of two or
more electrons, the value of the total angular momentum of these electrons results
from the coupling between the total → orbital angular momenta
of the electrons and the total → spin angular momenta of
the electrons. In this scheme the orbital angular momenta
and spin angular momenta of electrons are added separately to give
the total angular momentum L = Σ_{i} l_{i} and the
total electron spin angular momentum S = Σ_{i} s_{i}.
These are then added to give J = L + S.
Also called → LS coupling.
See also → jj coupling.

After Henry Norris Russell (1877-1957) and Frederick Albert Saunders (1875-1963),
American astronomers (1925, ApJ 61, 38); → coupling.

spin-orbit coupling

جفسری ِ اسپین-مدار، جفتش ِ ~

jafsari-ye espin-madâr, jofteš-e ~

Fr.: couplage spin-orbite

1) Astro.: A relationship between the orbital period of one body around another
and its rotational period on its axis. The relationship results from tidal forces
between the two bodies. For example, the rotation period of the Moon equals its revolution
period around the Earth.
2) Quantum mechanics:
The interaction between a particle's → spin angular momentum
and its → orbital angular momentum.

In a system composed of one celestial body orbiting another, the synchronization of the
orbital and rotational motions of the two bodies under the action of
→ tidal forces. For example, Pluto is tidally coupled to
its moon Charon. As for the → Earth-Moon system,
billions of years from now, the Earth and the Moon will have the same period of
rotation, and these will also exactly equal the orbital period of the
Moon around the Earth. → tidal friction.