Vibronic coupling to T1 and T2 vibrations and the Jahn-Teller effect in transition-metal exchange tetraclusters

A study has been made on the four-center Jahn-Teller effect in tetrahedral transition-metal tetraclusters of M₄X₄L₄ and M₄OX₆L₄ types (M metal, X and L ligands) for twofold orbital degeneracy at each of the four centers and strong coupling between the electronic states there and the cluster vibrations. An analytic expression is derived for the adiabatic potential in the space of all active vibrations. The features of the adiabatic-potential sheets in the T₁ and T₂ vibration space are examined, and the spectrum is derived for the lowest vibronic states. There is a qualitative discussion of the system dynamics.Translated from Teoreti-cheskaya i Éksperimental'naya Khimiya, Vol. 23, No. 6, pp. 657–665, November–December, 1987.