Abstract
The sum frequency generation (SFG) spectrum of and modes in the self-assembled monolayer of octadecanethiol is modeled in order to understand the reasons of the very low SFG intensity of modes and to investigate quantitatively the two types of L-shaped conformations qualitatively suggested in the literature. 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 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.
8 More- Received 12 January 2009
DOI:https://doi.org/10.1103/PhysRevB.79.125433
©2009 American Physical Society