The adsorption of naphthalene molecules on a Si(1 0 0)-2 × 1 surface at room temperature is investigated using infrared reflection absorption spectroscopy in the multiple internal reflection geometry (MIR-IRAS). To determine the adsorption configurations on the surface in detail, IRAS spectra in the C-H stretching vibration region are analyzed in comparison with frequency calculations based on a density functional theory method (DFT). As a result, naphthalene molecules adsorb on the surface in different manners depending on the surface coverage of the molecule. At low coverage, a single configuration is favored, in which the 1,4,5,8 carbon atoms of the molecule are bound to the dangling bonds of two adjacent Si dimers to form Si-C σ bonds. At high coverage, it adsorbs in several different configurations. This exposure-dependence is discussed in relation to intermolecular interaction on the basis of the calculations for models in which two naphthalene molecules adsorb on a Si cluster.
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