Spectroscopic evidence against tetra-σ adsorption configurations of on Ge(1 0 0)

Adsorption of C 2 H 2 molecules on a Ge(1 0 0) surface at room temperature have been studied by ultraviolet photoelectron spectroscopy (UPS) using synchrotron radiation. In the UPS spectra, molecular orbitals (MOs) of the adsorbed C 2 H 2 as well as the Ge–C bonding states were identified. After annealing the C 2 H 2 -adsorbed surface causing partial desorption of the molecules, all the MOs were found to remain intact. In particular, the persistence of the π C – C orbitals after partial desorption comprises firm spectroscopic evidence against the existence of the so-called tetra-σ-bonded structure of the adsorbed C 2 H 2 molecules.