It was recalled that the H2- ion in this oxide was paramagnetic and exhibited an isotropic electron paramagnetic resonance spectrum at temperatures above 13K. Below this temperature, the defect symmetry was tetragonal; with <001> as the symmetry axis. Here, the electron paramagnetic resonance spectrum of H2- in a stressed sample at 13K had the same symmetry and spin-Hamiltonian parameters as those of unstressed samples at 4K. The existence of strain led to a preferential alignment of the centers along the stretch axis, <001>. Superhyperfine interaction with the magnetic 43Ca isotope in the [001] plane indicated that |A| = 11.0MHz and |A||| = 9.1MHz, with the symmetry axis along <100> or <010>. A model which was consistent with the results was suggested to be that of a T1u ground state, with the degeneracy being lifted by a static tetragonal Jahn-Teller distortion of the lattice which became apparent at temperatures below 13K.

S.C.Ke, H.T.Tohver: Physical Review B, 1995, 52[13], 9387-91