Hyperfeinwechselwirkungen

Hyperfine interaction is a small perturbation in atomic, ionic, and molecular systems arising from the interaction between the magnetic moments of atomic nuclei and the magnetic field produced by the electrons. It also includes interactions of nuclear electric quadrupole moments with electric field gradients in the electronic environment. This interaction splits otherwise degenerate energy levels into closely spaced hyperfine levels, producing hyperfine structure in spectra.

The dominant component is magnetic dipole coupling, often described by a constant A, which governs the energy shift proportional to I·J. For nuclei with spin I ≥ 1, electric quadrupole coupling, described by a constant B, adds further shifts depending on the orientation of the nuclear quadrupole moment with respect to the electronic field gradient.

In atoms with one valence electron, the Fermi contact interaction provides a large part of the dipole coupling for s-electrons, while the dipole-dipole interaction contributes for higher-l electrons. In molecules, hyperfine effects reflect the distribution of unpaired electron density at the nucleus and can reveal bond character and conformation.

Hyperfine structure is central to several technologies: the 21 cm line in neutral hydrogen results from a ground-state hyperfine transition; atomic clocks use hyperfine transitions, notably the cesium-133 transition that defines the second; NMR and EPR rely on hyperfine interactions to provide chemical and electronic structure information.

In spectroscopy, resolution of hyperfine components enables precise determination of nuclear magnetic moments, isotopic shifts, and electron-nuclear coupling constants.

Hyperfine interactions are described by coupling constants A and B, and require quantum mechanical treatment with total angular momentum F = I + J, leading to energy levels split according to F values.