An Etymological Dictionary of Astronomy and Astrophysics

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.

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