VIBRONIC INTENSITIES IN CENTROSYMMETRIC COORDINATION-COMPOUNDS OF THERARE-EARTHS .2. A VIBRONIC CRYSTAL FIELD-CLOSURE-LIGAND POLARIZATION MODEL AND APPLICATIONS TO THE PRCL63- AND UBR62- COMPLEX-IONS IN OCTAHEDRAL SYMMETRY

A symmetry adapted formalism to evaluate the vibronic intensities indu ced by the ungerade vibrational modes in centrosymmetric coordination compounds of the rare earths is put forward and applied to several sel ected electronic transitions of the PrCl63- and UCl62- complex ions in octahedral symmetry. This current model is based upon a modified symm etry adapted version of the combined vibronic crystal field-closure-li gand polarisation approach. This model differs from that developed in Part I of this series, in that for the vibronic crystal field contribu tion to the total transition dipole moment, the closure procedure is e mployed rather than the utilisation of a truncated basis set for the c entral metal intermediate electronic states. A criterion is introduced to choose an appropriate set of phases for both the electronic and th e vibrational coordinates so that to ensure the right sign for the int erference term (which couples together both the vibronic crystal field and the vibronic ligand polarisation contributions to the total trans ition dipole moment). We have focused our attention on the modulation of the intermolecular force field and a version of a modified general valence force field has been adopted. The reasons for using this forma lism rather than the superposition model (SM) are fully discussed in t he text. Finally, it is shown that the agreement with experiment is sa tisfactory for most of the components of the transitions studied, desp ite the apparent simplicity of our model calculation. General master e quations applicable to any f(N) electronic configurations are derived to show the utility and flexibility of this current formalism.