We have investigated the adsorption of benzene C2H6 on Si(100)(2×1) surface at room temperature, using infrared absorption spectroscopy (IRAS) with multiple internal reflection geometry (MIR). To determine the detailed adsorption structure of benzene on the surface, we measured IRAS spectra in the C-H stretching vibration region and compared the measured C-H vibration frequencies of the adsorbed benzene molecule with the calculated ones obtained on the basis of the so-called hybrid density-functional theory (DFT). We confirmed that the benzene molecule nondissociatively adsorbs onto dimers on the surface. We found that benzene adsorbs in different manners, depending on the surface coverage of benzene. At low coverage the molecule adsorbs on the surface to favor the formation of benzene adsorbed on two adjacent dimers. On the other hand, at high coverage, the molecule adsorbs on the Si surface to generate benzene that adsorbs on a single dimer.
