Orbital disproportionation

In contrast to the JT case, where the possible distortion is restricted by the JT active modes only, the PJT-induced distortion may be of any kind, depending on the symmetries of the mixing states. Another distinguished feature of the excited-state PJT-induced distortion is that it leads to orbital disproportionation discussed in Sect. 4. 

The PJTE in excited states of systems with electronic configurations, which produce global minima with distorted geometries and orbital disproportionation (see below), was confirmed also by ab initio calculations of a series of molecular systems from different classes, including SisC, Siq, Naq", and Q1F3 [16],... 

The tiu configuration was also explored in the fullerene anions Ceo - For this system the orbital disproportionation (see Sect. 5) was first revealed by Ceulemans, Chibotaru, and Cimpoesu [25,26] by direct estimation of the electron interactions in the distorted configuration in order to explain the origin of conductivity in the alkaline-doped fullerides A3C60. 

A quite similar effect takes place in the case of electron configurations t. In this case the PJT strong vibronic mixing of two excited states and T2 results in a lower orbitally disproportionate component of the type tx f) ... 

Another illustration of the role of the JTE in rationalization of the results of ab initio calculations is the APES (discussed above) of the ground and first two excited states of the Sis molecule the cross section of which is shown in Fig. 4 [16]. Presently, just the picture of this APES and the numerical values of its parameters, without further rationalization, may not be sufficiently informative, even for a journal publication the only model to fully explain this picture is the JTE. The picture reveals a very weak JTE in the excited E state in combination with the PJTE on the two excited states E and M1 accompanied by orbital disproportionation (and no Berry phase factor) which together provide for a sufficiently full understanding of the results of the ab initio calculations. 

Keywords Jahn-Teller Effect Configurational instability Calculations Orbital disproportionation Spin crossover... 

As follows from these results, orbital disproportionation in systems with half-closed-shell electronic configurations is necessarily accompanied by lowering the spin of the electronic ground state. For the configuration it means transition from the high-spin (HS) triplet A state to the low-spin (LS) singlet state A, while for t this transition is from the quadruplet (HS = 3/2) to the doublet (LS = 1/2) state. Since this transition is induced by the PJT distortion originating from an excited... 

P Garcia-Femandez, I. B. Bersuker, and J. E. Boggs, Orbital disproportionation and spin-crossover as a pseudo Jahn-Teller effect, J. Chem. Phys. 125, 104102/11 (2006). 

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