Stark effect

Computed energy level spectrum of hydrogen as a function of the electric field near n = 15 for magnetic quantum number m = 0. Each n level consists of n degenerate sublevels; application of an electric field breaks the degeneracy. Energy levels can cross due to underlying symmetries of motion in the Coulomb potential.

The Stark effect is the shifting and splitting of spectral lines of atoms and molecules due to the presence of an external electric field. It is the electric-field analogue of the Zeeman effect, where a spectral line is split into several components due to the presence of the magnetic field. Although initially coined for the static case, it is also used in the wider context to describe the effect of time-dependent electric fields. In particular, the Stark effect is responsible for the pressure broadening (Stark broadening) of spectral lines by charged particles in plasmas. For most spectral lines, the Stark effect is either linear (proportional to the applied electric field) or quadratic with a high accuracy.