Stark Effect

In-depth explanation of Stark Effect

The Stark effect is the shift and splitting of spectral lines of atoms or molecules when they are placed in an external electric field. Unlike the Zeeman effect, which depends on magnetic quantum numbers, the Stark effect depends on the electric field strength and on the orbitals involved. It is used to analyse electric fields in plasmas and to measure the dipole moments of molecules. In hydrogen the shift is linear in the field for excited levels because of their degeneracy, whereas the ground state shows only a small quadratic shift. It is a useful diagnostic tool in astrophysics.

Going deeper: Stark Effect

Key ideas: An electric field shifts and splits spectral lines, with linear shifts for hydrogen (because of degenerate levels) and quadratic for most atoms. For hydrogen the linear shift grows with n, about 3 n (n1 - n2) e a0 E / 2, where n1 and n2 are parabolic quantum numbers. It arises from mixing states of opposite parity.

Common mistakes and connections: Students confuse it with the Zeeman effect: Stark is electric, Zeeman is magnetic. Another error is believing that ground-state hydrogen has a linear shift (it is quadratic). The effect is used to measure molecular dipole moments in rotational spectroscopy and in plasma diagnostics. It shows that orbitals can be polarized.

Visualization of Stark Effect

Hydrogen n=2 levels split linearly with electric field strength, an electric analogue of the Zeeman effect. The interactive lesson shows this as a live animation or chart.

Worked example and use case

In hydrogen the n = 2 levels split linearly with electric field strength because they are degenerate, while many other atoms show a quadratic shift.

Where Stark Effect fits in Atomic Structure & Periodicity

Stark Effect is topic 114 of 115 in Atomic Structure & Periodicity.

Related topics

• Magic NumbersAdvanced
• Island of StabilityAdvanced
• Zeeman EffectAdvanced
• Term SymbolsAdvanced

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