Epikemel principle

According to the Htickel model proposed by Ceulemans and Fowler, the two extra n electrons of the neutral TigC are accommodated in a triply degenerate orbital with t symmetry. Such a situation is susceptible to geometric instability of the Jahn-Teller type. Rather than considering a small deformation toward the trigonal symmetry predicted from the epikemel principle to be the most stable,... 

For electronic orbital doublets the two patterns, corresponding to odd and even n, constitute the only possibilities. Hence the epikemel principle for E terms may be further specified as follows ... 

Interestingly in some of these T type systems, there is evidence for a plasticity effect [48,55]. Furthermore in the case of Fe ( 0)4, interconversion of isomers may be induced by infrared laser irradiation [56]. Such observations corroborate the warped trough model of JT surfaces, on which the epikemel principle is based. 

From this it should be clear that the epikemel principle refers to the particular synunetry breaking properties of chemically relevant JT hamiltonians. Particularly, it does not claim that molecules in non-degenerate states should have maximal symmetry. 

A general analysis of the linear G x (g + h) problem has been carried out recently. The results fully confirm the epikemel principle. Ceulemans A, Fowler PW (1989) Phys. Rev. A 39 481... 

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