Interfacial structures and vibrational spectra at liquid/liquid boundaries: Molecular dynamics study of water/carbon tetrachloride and water/1,2- dichloroethane interfaces

Flexible and polarizable molecular dynamics simulations are carried out to elucidate the structure and vibrational sum frequency generation (SFG) spectra of two water/organic liquid interfaces: water/carbon tetrachloride (CCl ₄) and water/1,2-dichloroethane (DCE). Preceding experimental spectra by Richmond and co-workers have shown quite contrasting features of the two SFG spectra. The former spectrum is analogous with that of water/vapor interface with two-band structure, while the latter is structureless without feature of the dangling OH bond. The present calculations well reproduced these experimental features, though the orientational structure of interfacial water is found to be qualitatively similar. The structureless spectrum of the water/DCE is elucidated with considerable local interaction between water and DCE molecules at the interface, which results in red shift and broadening of the dangling OH band of the interfacial water directing toward the DCE phase.