Vibrational Sum Frequency Spectroscopy and Molecular Dynamics Simulation of the Carbon Tetrachloride-Water and 1,2-Dichloroethane-Water Interfaces

Vibrational sum frequency (VSF) spectra calculated using molecular dynamics (MD) simulations are compared with VSF experimental spectra to gain a clearer picture of water structure and bonding at the carbon tetrachloride-water (CCl4-H2O) and the 1,2-dichloroethane-water (DCE-H2O) liquid-liquid interfaces. The VSF spectral response from interfacial water at the CCl4-H2O interface contains spectral features similar to the resonant VSF response of the vapor-water interface and alkane-water interfaces, while the VSF spectrum from the DCE-H2O interface has a low signal with no distinguishing OH stretch spectral features. These MD based spectral calculations show how different bonding interactions at the DCE-H2O interface lead to spectral broadening, frequency shifting, and spectral interferences that are responsible for the difference in the experimentally measured DCE-H2O and CCl4-H2O spectra. The computational results show that weak H2O-H2O interactions are perturbed by the presence of DCE, leading to increased water penetration into the more organic-rich portion of the interfacial region and strong orientation of these penetrating water molecules relative to the CCl4-H2O interface. Strong H2O-H2O interactions at the interface are not significantly impacted by the presence of DCE.