Inorganic chemistryLesson 2 of 3 in the course Crystal field and ligand field theory

Jahn–Teller Effect: Symmetry, Vibronic Dynamics, and Applications

5 flashcards · 5 quiz questions · 5 match pairs · 5 fill-in sentences · English

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Summary

Degenerate states are distinct electronic states with the same energy. In a nonlinear molecule, an electronically degenerate ground state can make a high-symmetry geometry unstable. The nuclei can move along a symmetry-lowering distortion, split the degenerate states, and lower the system’s total energy. This spontaneous lowering of symmetry is the Jahn–Teller effect, also called Jahn–Teller distortion.

All flashcards

Electronic degeneracy
Two or more distinct electronic states have the same energy.
Octahedral Cu(II) and the Jahn–Teller effect
Cu(II) has a d9 configuration; uneven occupancy of its degenerate eg orbitals commonly leads to tetragonal distortion.
Jahn–Teller-active vibration
A vibration whose symmetry allows it to split an electronically degenerate state.
Ham reduction factor
A factor describing how dynamic Jahn–Teller coupling reduces measured orbital observables.
Cooperative Jahn–Teller effect
Interactions among local distortions in a crystal produce a long-range structural change.

Quiz questions

  1. For an electronic E doublet in cubic symmetry, which vibration can split the degenerate levels?Answer: A doubly degenerate e vibration
  2. In the ideal linear E ⊗ e Jahn–Teller model, what is the shape of the lower-surface minima?Answer: A circular set of equivalent minima around the high-symmetry point
  3. What can cause a pseudo Jahn–Teller distortion when electronic states are not exactly degenerate?Answer: Vibronic coupling strong enough relative to the energy gap and restoring forces
  4. What characterizes a static Jahn–Teller effect on the timescale of observation?Answer: The system remains localized in one distortion minimum
  5. What is a cooperative Jahn–Teller effect in a crystal?Answer: Interactions among local distortions produce a long-range structural change

Based on the Wikipedia article Jahn–Teller effect, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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