A molecular model for an excess electron in silicon: electron addition to hexatrimethylsilyl disilane, a derivative with eight -bonded silicon atoms

Abstract

Exposure of the hexatrimethylsilyl disilane to ionizing radiation at 77 K gave ESR (EPR) spectra including satellite features that are assigned to the radical anions . Similar features were obtained from dilute solutions in certain solvents known to promote electron capture. The results are analysed in terms of extensive delocalization within the seven Si - Si bonds, with a small preference for the central Si - Si bond. There is no case for invoking extensive use of the 3d silicon orbitals, the data being fully accommodated using the normal 3s + 3p orbitals of the framework. Similarly, using Freon as a solvent that promotes specific electron loss, the parent radical cations have been prepared by radiolysis. The ESR spectra are discussed in terms of distortions involving stretching of one or two specific Si - Si bonds. Thus, for this model compound, with seven Si - Si bonds, an excess electron is accommodated within the framework and is extensively delocalized. We suggest that these results lead to the conclusion that the conduction band for pure silicon is also based on the framework and that the more diffuse set of 3d orbitals do not make a major contribution.