Abstract

The theory of vibronic coupling in centrosymmetric complex ions, such as the LnX(6)(3-) species, which ocurrs in the hexachloroelpasolite Cs(s)NaLnX(6) (where Ln(+3) is a trivalent lanthanide ion and X= cl- or Br-), is presented within the framework of a combined vibronic crystal field-ligand polarization method. We consider a truncated expansion for the intermediate states and general equations are given to calculate the vibronic intensity distribution associated with a parity forbidden but vibronically allowed electronic transition. Both the vibronic crystal field ante the vibronic ligand polarization coupling constants are evaluated using a standard set of the symmetry coordinates. Special care concerning the phases of the symmetry coordinates and vibronic operators is necessary to ensure the correct signs for the cross terms, wich couple together both the vibronic crystal field and ligand polarization cintribution to the total transition dipole moment. The procedure is applicable to any f(n) central metal electron configuration