15min:

V. BOUDON, M. REY, M. LOËTE, F. MICHELOT, Laboratoire de Physique de l'Université de Bourgogne, UMR CNRS 5027, 9 Av. A. Savary, BP 4780, F-21078 DIJON Cedex, FRANCE.

Some transition-metal hexafluorides like ReF₆, OsF₆ or IrF₆ have the particularity to posses a incomplete electronic subshell leading to low-lying degenerate electronic states. The ground electronic state is generally also degenerate. This implies the existence of very complex rovibronic couplings and thus the observation of unsual spectra^,

A few years ago, we have elaborated a tensorial formalism adapted to octahedral molecules with an odd number of electrons ( i.e.\/ with half-integer angular momenta), defining the O_h^S group as the octahedron point group with its spinorial representations. We also presented a systematic tensorial development in the SU(2)øtimes C_I\supset O_h^S group chain for the vibronic Hamiltonian of an octahedral molecule in a fourfold degenerate electronic state of symmetry G'_g. However, this development had the disadvantage to lead to infinite matrices, due to the particular form of the vibronic coupling terms (Jahn-Teller, ... ). Moreover, the molecular rotation was not included. In this talk, we present a systematic tensorial development of the full effective rovibronic Hamiltonian for a given vibronic polyad in a G'_g electronic state. A construction of the form H=\sum_i t_i ((E^( _e)øtimes V^( _v))^( )øtimes R^( ))^(A_1g) is proposed, where we define electronic operators E^( _e). This Hamiltonian has now finite matrices in the basis of the considered polyad. A similar construction is also given for the transition moment operators (dipole moment and polarizability) which are necessary to calculate transition intensities.