Adsorption structure of cyclopentene on InP(001)(2x4)

We have studied the interface formation between cyclopentene and (2x4) reconstructed InP (001) surfaces by soft x-ray photoemission spectroscopy, reflectance anisotropy spectroscopy (RAS), and ab initio theory. After preparation of an uncontaminated (2 x 4) reconstruction under ultrahigh vacuum conditions, the surface was exposed to cyclopentene as monitored by RAS. The changes in the In 4d, P 2p, and C 1s core-level emission lines upon molecule adsorption indicate a covalent bonding of cyclopentene to the topmost atoms of the surface at two different bonding sites. Based on these results, a structure model is suggested, which is supported by ab initio calculations of the total-energy, the RAS signature, and the In 4d and P 2p core-level shifts. Our results suggest that the cyclopentene adsorption is a two-step process: first cyclopentene adsorbs on the "mixed dimer" and second the changes in the surface structure enable the additional adsorption on the second layer In-In surface bond.