Teoreticheskaya i Eksperimentalnaya Khimiya vol:20 pages:1-8
The authors present a study of the adiabatic potential surface of tetrahedral clusters in which each metal ion is located in an orbital doublet state. The investigation is restricted to consideration of the subspace of E vibrations, which are the ones of most current interest in the Jahn-Teller effect. In contrast to the usual Jahn-Teller problems, this problem is more complicated due to the large size of the electronic basis (2 4) of the interacting vibronic centers and the numerous vibrations which are active in the vibronic couplings. From the results obtained it follows that the shape of the surface for the lower sheet of the adiabatic potential for the cluster in the E vibration space is similar to the surface for the E-e problem both in the linear and in the quadratic cases. The average values of the pseudospin operators in the vibronic ground states are the same for all centers, which is evidence (taking into account the equality of the Jahn-Teller distortions at all centers) for ferrodistortion ordering of all the distortions, both in the linear and in the quadratic cases. If each vibronic center has spin s=1/2, all vibronic levels of the cluster have additional 16-fold spin degeneracy. The indicated orbital and spin accidental degeneracy of the sheets is removed by taking into account the intercenter interaction.