The geometry and chemical interactions of c-C5H8 after adsorption on a Si(001), surface were analyzed using density functional theory calculations. Using a slab model, a study was made of the changes in the atomic and orbital interactions corresponding to the system. Overlap population values were examined for specific bonds during the adsorption. Two cases were considered: cyclopentene adsorption on dimers at the surface and on dimer vacancies on Si(001). An average =C-Si distance of 1.96Å was found on dimer Si-Si; and average H-Si, -C-Si and =C-Si distances of 1.59, 1.83 and 1.57Å, respectively, on dimer vacancies. The density of states and the crystal orbital overlap populations corresponding to C-C, C-Si, C-H and Si-Si bonds were also studied. The main contribution to the adsorption were the C=C double bond in both cases and the H atoms belonging to this double bonds in the case of adsorption on dimer vacancies. The orbital contribution included participation of the 2pz orbitals corresponding to C atoms and 3pz orbitals corresponding to Si in the case of adsorption on Si(001)-2 x 1 surface, and 2px, 2py and 2pz orbitals corresponding to C atoms, and the 3px, 3py, and 3pz orbitals corresponding to Si for cyclopentene adsorption on dimer vacancies. The adsorption of cyclopentane on Si(001)-2x1 produced several vibrational frequencies similar to that of c-C5H10, a molecule with sp3 hybridization. After . C5H8 adsorption no frequencies coming from a C=C bond were computed which also supported the idea of re-hybridization. On dimer vacancies, the Si-C frequency increased 35/cm, indicating a stronger bond with the surface.

Cyclopentene (c-C5H8) Adsorption on Si(001)-2x1 and on Dimer Vacancies on the Surface: a Theoretical Study of the Electronic Structure and Chemical Bonding. E.Germán, I.López-Corral, A.Juan, G.Brizuela: Computational Materials Science, 2010, 49[4], 888-94