The electron paramagnetic resonance (EPR) spectra of ␥-irradiated titania-bearing sodium silicate glasses were quantitatively analyzed by using the spectral decomposition of the EPR spectra and categorizing it into two types of randomly oriented paramagnetic centers: the orthorhombic (HC 1 ) center and the axially symmetric (HC 2 ) center. The orthorhombic HC 1 center was assigned to the Q 2 structural unit (the term Q i represents a SiO 4 tetrahedron with i bridging oxygens), whereas the generation of the axially symmetric HC 2 radical was expected in the case of the Q 3 unit. The relative amounts x(HC 1 ) and x(HC 2 ) of HC 1 and HC 2 radicals were evaluated using the obtained data of the measured EPR spectra for five ␥-irradiated glasses with titania contents in the range of 0-10 mol%. The strong increase of the HC 1 relative abundance, from a value of 26% (for titania-free glass) to a value of 89% (obtained for glass with 1 mol% of titania) confirmed the preferred sensitivity of Q 2 units at low titania contents. Thus, titanium, which has a great absorption cross section, preferably entered the positions in the neighborhood of the Q 2 units. The semi-empirical linear combination of atomic orbitals to form molecular orbitals by a self-consistent field (LCAO-MO-SCF) quasi-relativistic intermediate neglect of differential overlap (INDO) method was used to confirm this effect. For titania contents of >1 mol%, the abovementioned effect was overwhelmed by the structural changes induced by titania in the silicate network, namely the diminishing of the Q 2 content. Only the axially symmetric HC 2 centers were present in the glasses with titania contents of >5 mol%.
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