Inner-shell spectroscopy of compounds containing Si-Si bonds: is there a localised, low-energy Si-Si resonance?

Oscillator strengths for the Si 2p, Si 2s, and C 1s excitation of tetramethylsilane, hexamethyldisilane, tetrakis(trimethylsilyl)silane, and dodecamethylcyclohexasilane have been derived from electron energy loss spectra recorded in the dipole-regime. These results are compared to the Si l s and Si 2p photoabsorption spectra of tetramethylsilane, hexamethyldisilane, tris(trimethylsilyl)silane, and tetrakis(trimethylsilyl)silane, recorded using synchrotron radiation. The spectra support the existence of a localised, low-lying state of large Si-Si character in species which contain Si-Si bonds.