It was noted that the energy states of the neutral isolated self-interstitial, I0, exhibited a negligible linear response to perturbations. Uni-axial stress and isotope methods were combined here in order to study the interactions between the electronic states of I0. A fifth electronic state of the center was identified which exhibited 2 closely spaced doublets in the electronic energy level scheme of the defect. The I0 had a split-<001> structure. It was show that, in diamond, this configuration was highly susceptible to 2 independent symmetry-lowering distortions; via a B1 transformation to D2 in the ground state and via a B2 transformation to C2v in the excited state.

Mapping the Energy Levels of the Self-Interstitial in Diamond. H.E.Smith, G.Davies, M.E.Newton, H.Kanda: Physica B, 2003, 340-342, 111-5