Molecular distortions due to an electronically degenerate @[email protected] state. For non-linear molecular entities in a geometry described by a point symmetry group possessing degenerate irreducible representations there always exists at least one non-totally symmetric vibration that makes electronically degenerate states @[email protected] at this geometry. The nuclei are displaced to new equilibrium positions of lower symmetry causing a splitting of the originally degenerate states (first-order Jahn–Teller effect).
Effect due to the odd terms in the vibronic perturbation expansion. In the case of molecules with a non-degenerate @[email protected] but with a low-lying degenerate @[email protected], distortions of proper symmetry arise that result in mixing of the ground and excited states, thereby lowering the ground-state energy (pseudo Jahn–Teller effect). The pseudo Jahn–Teller effect manifests itself in @[email protected] behaviour (see @[email protected]) and @[email protected] of molecules and ions. The Jahn–Teller effect generates a @[email protected] (e.g., a @[email protected]) whereas a pseudo Jahn–Teller effect generates an @[email protected]
See also:
Renner–Teller effect
PAC, 2007, 79, 293. (Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)) on page 360 [Terms] [Paper]