Jahn-Teller symmetry change

This operator contains an odd and an even term in as there are no symmetry restrictions on the radial coordinate. The -dependent factor of the linear (Jahn-Teller) term changes sign if the angular coordinate changes by n, but the quadratic (Renner-Teller) term does not, as required for systems with a rotation axis C , where n is odd. It is often assumed that the quadratic term can be neglected. The problem then reduces to cylindrical symmetry and simplifies a great deal. We shall see, however, that the quadratic terms are qualitatively important in resonance Raman scattering. 

The static Jahn—Teller distortions appear as structural changes which may be associated with the origin of low symmetry terms in the ligand field potential. Here, the separation of the orbital... 

Richard Bader was among the earliest of workers to realize the importance of electron density in providing an understanding of chemistry. Early on he was led to formulate the first symmetry rule governing a chemical reaction in answer to the question of how the electron density changes in response to a motion of the nuclei. This rule, termed the pseudo- or second-order Jahn-Teller effect, provides the theoretical underpinnings of frontier molecular orbital theory and is still widely used in discussions of reaction mechanisms and molecular geometries. 

At the same time, as it is known, the molecular systems in the degenerated states are dynamically unstable with respect to symmetry distortions due to the Jahn-Teller effect [9]. Such kinds of distortions are expected both in the electronic and nuclear subsystems (vibronic instability). The Jahn-Teller effect destabilizes the tetrahedral geometry of the nuclear system, which results in the bond order s changes too. In particular, according to the theory of the Jahn-Teller effect [9] the tetrahedral molecular systems in the 2Ti(P ),lT2(Pi ) or 37 (P4 ) states are dynamically unstable to the e- and t2-type nuclear distortions, one of which is presented in Fig. 7.1 Evidently such a kind of distortion to the butterfly geometry... 

The most interesting possibility indicated by this phase diagram is that the FO phase may be present as a metastable phase below Tjt = 26 K, instead of the HS phase above rJT. It suggests that physical properties of the metastable phase may change at rJT. Recently, a photo-induced metastable phase of an Fe(II) spin-crossover complex [Fe(2-pic)3]Cl2 EtOH (2-pic = 2-aminomethylpyridine) was reported [26-28]. Its properties are remarkably different from those of the metastable HS phase quenched by rapid cooling. Lowered symmetry accompanying the Jahn-Teller deformation has... 

Let us now try to explain the observed lineshape and the large broadening at r=10 K. In the temperature range between 10 and 50 K the C60 ion by itself is static, i.e., it does not perform any sort of physical reorientation. However, the orientation of the Jahn-Teller distortion may change on a time scale comparable to the inverse 13C NMR linewidth, i.e., r =l/Av1/2 3 ns. A possible sequence of such pseudorotations between (symmetry allowed) competing orientations of the Jahn-Teller distortion are shown in Fig. 33. Molecular orbital calculations... 

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