Deriving the complete molecular conformation of self-assembled alkanethiol molecules from sum-frequency generation vibrational spectra

作者：Bourguignon Bernard^*; Zheng Wanquan; Carrez Serge; Ouvrard Aimeric; Fournier Frederic; Dubost Henri

来源：Physical Review B, 2009, 79(12): 125433.

DOI：10.1103/PhysRevB.79.125433

• ab initio calculations
• adsorption
• gold
• molecular configurations
• optical frequency conversion
• organic compounds
• self-assembly
• vibrational modes

The sum frequency generation (SFG) spectrum of CH2 and CH3 modes in the self-assembled monolayer of octadecanethiol is modeled in order to understand the reasons of the very low SFG intensity of CH2 modes and to investigate quantitatively the two types of L-shaped conformations qualitatively suggested in the literature. CH2 modes are assumed local in order to calculate easily the spectrum of any conformation, and ab initio molecular hyperpolarizabilities are used. It is found that the absence of CH2 bands does not imply an all-trans conformation and vice versa. Several conformations are compatible with SFG, but only one of them can be arranged on Au(111) and completely agrees with x-ray diffraction. All conformational details of the L-shape molecules are obtained.

• 出版日期2009-3