Qualitative MO treatment of the γ-induced paramagnetic centres in titania bearing sodium silicate glasses

The unusual behaviour of EPR spectra of γ-irradiated titania bearing sodium silicate glasses with various contents of titania were qualitatively interpreted on the base of model molecular orbital calculations. As a model of the actual paramagnetic particles were chosen the clusters which indemnify the reasonable compromise between the model of cluster and exactness of calculation used. The results of the quantum chemical calculations show the preferential sensibilisation of Q 2 unit in comparison with Q 3 unit (the largest electron density in the vicinity of non bonding oxygens in Q 2 model). The bond strengths of Si-O bonds in the neighbourhood of non-bridging oxygens show to the preferential substitution of Si 4+ for Ti 4+ in the vicinity of the boundary of the cluster. The changes of the spin density distribution around the cluster after substitution of Si 4+ for Ti 4+ (the largest delocalization) explain the unusual behaviour of the g-tensor component with titania content in the glasses.