Jahn-Teller interaction

Local and cooperative Jahn-Teller interactions in model structures. D. Reinen and C. Friebel, Struct. Bonding (Berlin), 1979, 37,1-60 (136). 

Reinen D, Friebel C (1979) Local and Cooperative Jahn-Teller Interactions in Model Structures. Spectroscopic and Structural Evidence. 37 1-60 Reinen D (1970) Kationenverteilung zweiwertiger 3dn-Ionen in oxidischen SpineU-, Granat und anderen Strukturen. 7 114-154... 

A determined search for superconductivity in metallic oxides was initiated in mid-summer of 1983 at the IBM, Zurich Research Laboratories in Riischliken, Switzerland. This research effort was an extension of previous work (145) on oxides, namely, Sr1.xCaxTiOs, which exhibited some unusual structural and ferro-electric transitions (see Section 2.2a). During the summer of 1983, the superconductivity research was focussed on copper-oxide compounds. Muller had projected the need for mixed Cu2+/Cu3+ valence states, Jahn-Teller interactions (associated with Cu2+ ions), and the presence of room temperature metallic conductivity to generate good superconductor candidates. These researchers then became aware of the publication by Michel, Er-Rakho, and Raveau (146) entitled ... 

The higher vibronic components of the E state are split by the linear Jahn-Teller interactions, leading then to the splitting of those hot bands in the spectrum which correspond to the coupling e vibration. 

One well-known example of the physical system where the described approach can be applied is the Aj-E optical transition in trigonal centers with the E-e-type Jahn-Teller interaction. In this case the AP in the electronic E-state has a shape of the Mexican hat [11 -14]. If the E-e-type Jahn-Teller interaction is strong, then the Mexican hat is large and the AP has a long minimum line along the trough. In this... 

If there are several AP minima of close energy, then at low temperatures one should take into account two-phonon-assisted transitions between these minima. In Ref. [15] (see also Ref. [14]) it was found that the rate of these transitions depends on temperature as 7 3. However, as it was already mentioned above, in Ref. [9] it was found that the contribution of the two-phonon-assisted transitions between different Jahn-Teller minima of the AP to the ZPL width at low temperatures is described by the T5 law. Note that an increase of the Jahn-Teller interaction leads to a decrease of the rate of these transitions. Therefore, in the strong Jahn-Teller interaction limit this broadening mechanism becomes unimportant. 

The nature of the Jahn-Teller interaction is such as to yield several vibronic states, within just a few wave numbers of the ground state. These states have very different expectation values for the electronic and nuclear co-ordinates, and we shall now examine how the low-lying vibronic structure may be elucidated by the followings modem physical techniques high-field, multifrequency electron paramagnetic resonance (HFMF EPR) magnetic circular dichroism (MCD), and extended X-ray absorption fine stmcture spectroscopy (EXAFS). The recent advent of HFMF EPR... 

Fig. 8 Contribution to the effective repulsion between electrons from the Jahn-Teller interaction (arbitrary units). (Adapted from [16])...

Lim EC (1986) Proximity effect in molecular photophysics Dynamical consequences of pseudo-Jahn-Teller interaction. Journal of Physical Chemistry 90 6770-6777. 

Small metal clusters have received considerable attention because of their possible involvement as "active sites" in a variety of catalyzed reactions. Although not particularly noted for their catalytic activity, alkali clusters have a simple chemical composition and may, therefore, model the more complicated systems in a manner analogous to the role played by the hydrogen atom in atomic structure. Less emphasized is the fundamental nature of alkali clusters per se. Since the ground state of Hj is not chemically bound, alkali trimers are the most elementary species which can exhibit a Jahn-Teller interaction. 

One approach of this type is due originally to Bader, who used perturbation theory to show that unimolecular reaction is particularly favoured along a normal co-ordinate whose symmetry is the same as that of the transition density between the ground state and a low-lying excited state, because then second-order Jahn-Teller interaction depresses the energy of the ground state. The idea has been taken up by Salem and Pearson and used, in conjunction with a semilocalized MO model, to determine the allowed routes in the pyrolysis of cyclobutane and cyclohexene. Fukui et a/. have described a similar method. 

Reinen, D., Friebel, C. Local and Cooperative Jahn-Teller Interactions in Model Structures. 

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