THE JAHN-TELLER EFFECT IN THE EXCITED-STATES OF MNF64- AND CRF63- COMPLEXES

The coupling coefficient, V-E, with the Jahn-Teller mode, E(g), for th e first excitations of MnF64- and CrF63- complexes has been investigat ed through Molecular Orbital calculations for different values of the tetragonal Q(theta) coordinate. The present analysis reveals that the stable geometry for the first excited state of MnF64- (T-4(1)) and CrF 63-(T-4(2)) is that of an elongated and compressed octahedron respecti vely. The calculated values for MnF64- at the equilibrium distance (R = 212 pm) of RbMnF3 are close to the experimental value V-E = 65 cm(-1 )/pm. As a salient feature it is shown that V-E proportional to R(-p) (p being close to six) and thus it exhibits the same dependence as the coupling coefficient, VA, With the symmetric mode. Finally, the prese nt analysis predicts an increase of the Stokes shift upon increasing R provided the Gruneisen constant is higher than two. It thus explains recent experimental data on Mn2+-doped fluoroperovskites.