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 (CCl 4 −H 2 O) and the 1,2-dichloroethane−water (DCE−H 2 O) liquid−liquid interfaces. The VSF spectral response from interfacial water at the CCl 4 −H 2 O 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−H 2 O 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−H 2 O interface lead to spectral broadening, frequency shifting, and spectral interferences that are responsible for the difference in the experimentally measured DCE−H 2 O and CCl 4 −H 2 O spectra. The computational results show that weak H 2 O−H 2 O 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 CCl 4 −H 2 O interface. Strong H 2 O−H 2 O interactions at the interface are not significantly impacted by the presence of DCE.