An interaction between the orbital angular momentum and the spin angular momentum of an individual particle, such as an electron. For light atoms, spin-orbit coupling is small so that multiplets of many-electron atoms are described by Russell-Saunders coupling. For heavy atoms, spin-orbit coupling is large so that multiplets of many-electron atoms are described by j-j coupling. For medium-sized atoms the sizes of the energies associated with spin-orbit coupling are comparable to the sizes of energies associated with electrostatic repulsion between the electrons, the multiplets in this case being described as having intermediate coupling. Spin-orbit coupling is large in many nuclei, particularly heavy nuclei.
Subjects: Chemistry — Physics.