Interaction Geometry Causes Spectral Line-Shape Broadening at the Solid/Liquid Interface

Abstract

Line-shape broadness in vibrational spectra is usually associated with structural heterogeneity of the surrounding environment. At the solid/liquid interface, surface-sensitive sum-frequency generation spectroscopy (SFG) has shown a variety of distributions of the vibrational frequency for sapphire surface hydroxyl groups in contact with several liquids. Even though the broadness in SFG spectra could be associated with the surface heterogeneity and diverse interfacial interactions, the origin remains elusive in experiments. To better understand the physical picture of interfacial interactions, and hence broadness, we perform SFG along with molecular dynamics (MD) simulations of liquid molecules in contact with sapphire. In the SFG spectra, line-shape broadness of the sapphire hydroxyl group vibrational frequency increases in the following order: chloroform, acetone and dimethyl sulfoxide. The broadness in the interaction energy distributions calculated from the MD simulations for the molecules interacting...