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A distortion of a highly symmetrical molecule, which reduces its symmetry and lowers its energy. The effect occurs for all nonlinear molecules in degenerate electronic states, the degeneracy of the state being removed by the effect. It was first predicted in 1937 by H. A. Jahn and E. Teller. In early experimental work, the effect often “disappeared” or was masked by other molecular interactions. This has surrounded the Jahn-Teller effect with a certain mystery and allure, rarely found in science today. However, there are now a number of clear-cut experimental examples which correlate well with theoretical predictions. These examples range from the excited states of the most simple polyatomic molecule, H3, through moderate-sized organic molecules, like the ions of substituted benzene, to complex solid state phenomena involving crystals or localized impurity centers. See Crystal defects, Degeneracy (quantum mechanics), Molecular structure and spectra, Quantum mechanics
With the exception of linear molecules which suffer Renner-Teller effects, all polyatomic molecules of sufficiently high symmetry to possess orbitally degenerate electronic states will be subject to the Jahn-Teller instability. However, in cases other than molecules with fourfold symmetry, the proof is somewhat involved and requires the use of the principles of group theory. See Renner-Teller effect