LIGAND POLARIZATION VIBRONIC INTENSITIES IN THE ELECTRONIC-SPECTRA OFCENTROSYMMETRIC COORDINATION-COMPOUNDS OF THE TRANSITION-METAL IONS -THE CR(NH3)(6)(3+) ION IN THE OCTAHEDRAL POINT MOLECULAR GROUP

The observed spectral intensities of the various false origins associa ted with the (2)E(g) <---->(4)A(2g) phosphorescence of the hexamminech romium (III) ion have been rationalised on the basis of a dynamic liga nd polarization model. The most intense spectral features observed in the spectrum have been identified and assigned with both the tau(1u) ( N-Cr-N bending and Cr-N-H rocking) as well as tau(2u) (N-Cr-N bending and Cr-N-H rocking) species, which show up comparable intensities. The dynamic approach adopted has shown to be suitable to deal with both p olyatomic and highly polarizable ligands, such as the ammine groups. T hroughout the course of the present work, we have employed three diffe rent models: A seven; a thirteen and a twenty five atom system models, and the vibrational symmetry adapted vibrational wavefunctions utilis ed in this calculation have been built up using a consistent set of ph ases. It is shown that, when the seven atom system model is employed, a satisfactory agreement with experiment for the skeletal intensity ra tios f(v(3)):f(v(4)):f(v(6)) is achieved. We also found that the thirt een atom system model reproduces nicely the vibronic intensity distrib ution for both the skeletal and the framework-ligand coupling vibratio nal modes of motion for the system. A modest result is found for the t wenty five atom system model in both O-h and D-3d symmetries and the m ost likely reasons for this disagreement are discussed in the text.