HIGHER-ORDER VIBRONIC INTERACTIONS IN CENTROSYMMETRIC COORDINATION-COMPOUNDS OF THE TRANSITION-METAL IONS

In the present work, we consider diagonal and non diagonal higher thir d order vibronic interactions in coordination compounds of the transit ion metal ions. We develop a general approach, using perturbation theo ry for non degenerate electronic states up to third order correction. For illustrative purposes, this formalism is applied to the 2E(g) <-- --> 4A2g phosphorescence of the MnF6(2-) complex ion in a cubic enviro nment. For this excitation a complete set of experimental data is avai lable. Our vibronic model is developed within the framework of a combi ned crystal field-ligand polarization approach, and makes no allowance s to consider distortions along the Jahn-Teller active vibrational mod es of the MnF6(2-) complex ion. The necessary crudeness of this formal ism precludes an overall fair agreement with experiment and the discre pancies are analyzed on the basis of the simplications adopted. In spi te of the necessary crudeness of our model, a fair degree of success h as been achieved in the understanding of the spectral intensity mechan isms in centrosymmetric coordination compounds.