Orbitalbeitrag

Orbitalbeitrag is a term used in physics and chemistry to describe the portion of a measured quantity that originates from the orbital motion of electrons (or other charged particles) around a nucleus or within a solid lattice. It contrasts with contributions that arise from intrinsic spin, which is an independent form of angular momentum.

In quantum mechanics, the total angular momentum of an electron consists of orbital angular momentum L and spin angular momentum S. The orbital part can give rise to a magnetic moment μ_L that is proportional to L, typically expressed as μ_L = -μ_B (L/ħ), where μ_B is the Bohr magneton. The spin contribution μ_S is related to S, often written as μ_S = -g_s μ_B (S/ħ) with g_s close to 2. The combination of these contributions determines properties such as the overall magnetic moment and magnetic behavior of atoms, ions, and materials.

In solids and coordination complexes, the orbital contribution can be affected by the surrounding electric fields, known as crystal or ligand fields. In many systems, the orbital angular momentum is partially or largely quenched by these fields, reducing the orbital contribution. In others, especially in heavy elements with strong spin–orbit coupling or in systems with weak symmetry constraints, the orbital part remains significant and must be considered to explain measurements accurately.

Practically, the orbital contribution is often inferred or separated from the spin part through experimental techniques such as X-ray magnetic circular dichroism or neutron scattering, and it can influence quantities like magnetization, g-factors, and spectroscopic selection rules. See also orbital angular momentum, spin–orbit coupling, and magnetic moments.