CALCULATION OF THE JAHN-TELLER COUPLING FOR CR3- AN INSIGHT INTO OPTICAL-PROPERTIES( AND MN2+ IMPURITIES )

Self-Consistent Charge-Extended Huckel and MS-X alpha calculations on CrF63- and MnF64- complexes performed for several values of the Q(0) s imilar to 3z(2)-r(2) normal coordinate and for different values of the metal-ligand distance R have been carried out in order to calculate t he coupling coefficient, V-E, with the Vibrational Jahn-Teller mode E- g of orbitally triplet excited states. The equilibrium geometry of the T-4(2g) crystal-field state of CrF63- is shown to correspond to a com pressed octahedron. In this case the coupling to the Jahn-Teller mode explains about 50% of the experimental Stokes shift, and the rest come s from the contribution, V-A, due to the symmetric A(1g) mode. For MnF 64- the present calculations explain the sign and V-E values measured for T-4(1g)(G) and higher crystal-field excited states. Also the incre ase of the Stokes shift upon increasing R observed in MnF64- has been explained having in mind the strong R dependence displayed by both V-E and V-A as well as by the Gruneisen constant. As a salient result the R dependence of V-E and V-A has been shown to arise form the small am ount of 2s(F-) wavefunctions present in the antibonding e(g) orbital. Finally for charge-transfer bands of CrF63- V-A is shown to be much m ore important than V-E.