Molecular arrangement of ethylene on Si(001) surface by CAICISS

C$_{2}$H$_{4}$ molecules have been non-dissociatively chemisorbed on Si(001)-(2$\times $1) surface at room temperature with an exposure of 100L, and C$_{2}$H$_{4}$ on Si(001) surface structure has been investigated by coaxial impact collision ion scattering spectroscopy (CAICISS). To determine the adsorption structure of the C$_{2}$H$_{4}$ molecules definitely, the computer simulation with the 2-D trajectory count method has been performed for the recently proposed most possible two single molecular adsorption configurations (di-$\sigma$ on-top and di-$\sigma$ end-bridge). The CAICISS spectra and simulation results show that the di-$\sigma$ on-top structure is better fit than the di- $\sigma$ end-bridge structure. It is found that the bond length of Si dimer separation on the Si(001) surface with the adsorption of C$_{2}$H$_{4}$ is $2.35 \pm 0.05 $ \AA. This implies that the bonding of Si dimers stays intact. It is also found that the bonding length of C--Si and C--C is $1.81 \pm 0.05$ \AA\ and $1.61 \pm 0.05$ \AA\, respectively.