A type of coupling in systems involving many fermions. These systems include electrons in atoms and nucleons in nuclei, in which the energies associated with electrostatic repulsion are much greater than the energies associated with spin-orbit coupling. Multiplets of many-electron atoms with a low atomic number are characterized by Russell-Saunders coupling. It is named after the US physicists Henry Norris Russell (1877–1957) and Frederick Saunders (1875–1963) who postulated this type of coupling to explain the spectra of many-electron atoms with low atomic number in 1925. The multiplets of heavy atoms and nuclei are better described by j-j coupling or intermediate coupling, i.e. a coupling in which the energies of electrostatic repulsion and spin-orbit coupling are similar in size.
Subjects: Chemistry — Physics.