Ceder et al. recently used scanning tunneling electron microscopy to directly observe the cooperative version of this phenomenon in a sodium/manganese/O2 superstructure. The second-order variant of this phenomenon occurs to allow for a configuration interaction between a molecule's HOMO and LUMO and can be invoked to explain the stereoactive lone pair in xenon hexafluoride. A shoulder in the UV-Vis absorption band of aqueous titanium(III) is attributed to this phenomenon
Ceder et al. recently used scanning tunneling electron microscopy to directly observe the cooperative version of this phenomenon in a sodium/manganese/O2 superstructure. The second-order variant of this phenomenon occurs to allow for a configuration interaction between a molecule's HOMO and LUMO and can be invoked to explain the stereoactive lone pair in xenon hexafluoride. A shoulder in the UV-Vis absorption band of aqueous titanium(III) is attributed to this phenomenon, which often occurs in a weaker (*) dynamic form at room temperature in complexes with T-sub-1g and T-sub-2g ground states. This phenomenon is weak in tetrahedral complexes, since none of the ligands directly overlap with any d-orbitals. The most common manifestation of this phenomenon is in the tetragonal elongation of six-coordinate transition metal complexes with four, seven, or nine d- electrons. For 10 points, name this effect in which a molecule distorts to relieve an orbital degeneracy.
Ceder et al. recently used scanning tunneling electron microscopy to directly observe the cooperative version of this phenomenon in a sodium/manganese/O2 superstructure.
Jahn-Teller effect [or  Jahn-Teller distortion]