Jahn–Teller effect on the [TiF4F4Fint]6−(C4v) and [NiF4F4Fint]7−(C4v) clusters embedded into SrF2 crystals

By means of EPR method the associative [TiF4F4Fint]6−(C4v) and [NiF4F4Fint]7−(C4v) centers were revealed in the fluorite type SrF2:Ti and SrF2:Ni crystals grown by Bridgman method in helium atmosphere containing some amount of a fluorine gas. It was found that at low temperatures the local structures of these associative centers were exposed to a static rhombic distortion. The reasons of such distortions were accounted for by the assumption that the E ⊗ (b1 + b2) vibronic interaction became effective due to that the ground orbital states of the [TiF4F4Fint]6−(C4v) and [NiF4F4Fint]7−(C4v) centers occurred to be doubly degenerated.