Jahn-Teller effect

 The Jahn-Teller effect is a phenomenon in chemistry and physics that describes the relationship between the geometry of a molecule and its electronic energy. It was first proposed by Herbert Jahn and Edward Teller in 1937, and since then it has become a widely recognized and well-studied aspect of molecular physics.

The Jahn-Teller effect occurs when a molecule has a degenerate electronic state, meaning that there are multiple energy levels with the same energy. In such a situation, the molecule will often undergo a geometric distortion in order to lower its energy. This distortion allows the molecule to reduce its energy by splitting the degeneracy of the electronic state and creating distinct energy levels.

One of the key features of the Jahn-Teller effect is that the geometric distortion of the molecule can result in significant changes to its physical and chemical properties. For example, the distortion can cause a change in the bond length, bond angle, and overall shape of the molecule. These changes can have a major impact on the molecule's reactivity, stability, and spectral properties, such as its infrared and electronic spectra.

One of the most well-known applications of the Jahn-Teller effect is in the field of coordination chemistry, where it is used to explain the geometric distortions of coordination complexes. Coordination complexes are molecules that contain a central metal ion surrounded by ligands, which are typically other molecules or ions. In many cases, these complexes exhibit distorted geometries due to the Jahn-Teller effect, which can have a major impact on their properties and reactivity.

In addition to its applications in coordination chemistry, the Jahn-Teller effect has also been studied in other areas of chemistry and physics, such as inorganic and organic chemistry, solid-state physics, and quantum mechanics. It has been used to explain the behavior of transition metal complexes, electronically excited states, and photo-induced processes, among other things.

In conclusion, the Jahn-Teller effect is a fundamental aspect of molecular physics and chemistry that has been widely studied and applied to a wide range of chemical and physical systems. Its impact on the geometric and electronic structure of molecules has led to a better understanding of their properties and reactivity, and has provided new insights into the nature of chemical bonds and the behavior of electronic systems.