Surface reactions of 3-butenenitrile on the Si(001)-2 x 1 surface at room temperature

Using a combination of local -- scanning tunneling microscopy -- and spatially integrated, but chemically sensitive probes -- X-ray photoelectron spectroscopy and near edge X-ray absorption fine structure spectroscopy -- we have examined how 3-butenenitrile reacts with the Si(001)-2 x 1 surface at room temperature. Electron spectroscopies indicate three different nitrogen chemical bonds: a Si-C=N-Si bond, a C=C=N cumulative double bond, and a CN moiety datively bonded to a silicon atom. All molecular imprints detected by scanning tunneling microscopy (STM) involve two adjacent silicon dimers in the same row. The three geometries we propose -- a double di-sigma bonding via the CN and the C=C, a cumulative double bond formation associated with alphaC-H bond dissociation, and a di-sigma vinyl bonding plus a CN datively bonded to a silicon atom -- are all compatible with electron spectroscopies and data. Real-time Auger yield kinetic measurements show that the double di-sigma bonding geometry is unstable when exposed to a continuous flux of 3-butenenitrile molecules, as the Si-C=N-Si unit transforms into a CN moiety. A model is proposed to explain this observation.