The primary goal of spectroscopy is to obtain molecularly detailed information about the system under study. Sum frequency generation (SFG) vibrational spectroscopy is a nonlinear optical technique that is highly interface specific, and is therefore a powerful tool for understanding interfacial structure and dynamics. SFG is a second order, electronically nonresonant, polarization experiment and is consequently dipole forbidden in isotropic media such as a bulk liquid. Interfaces, however, serve to break the symmetry and produce a signal. Theoretical approximations to vibrational spectra of O-H stretching at aqueous interfaces are constructed using time correlation function (TCF) and instantaneous normal mode (INM) methods. Detailed comparisons of theoretical models and spectra are made with those obtained experimentally in an effort to establish that our molecular dynamics (MD) methods can reliably depict the system of interest. The computational results presented demonstrate the potential of these methods to accurately describe fundamentally important systems on a molecular level.

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