Organic materials play an important role in atmospheric processes especially in conjunction with aerosols. Vibrational sum-frequency spectroscopy (VSFS), an interface sensitive technique, gives insight to the behavior of organic materials adsorbed on aerosol surfaces. Due to the nature of the VSFS response in experiments, some specific molecular information may be impossible to obtain.  Therefore, vibrational sum-frequency spectra for a set of atmospherically relevant organic molecules at an air/water interface are calculated and compared to experimental VSFS data. A combination of molecular orientations and conformations from classical molecular dynamics as well as second order linear susceptibilities from time dependent density functional theory are used to determine theoretical VSFS spectra. In the initial model, spectra are calculated using static conformations and orientations. Improvements to the initial model are made in a methodical fashion and the effects of each change are detailed. Comparisons with experimental spectra are used to determine which assumptions are valid and the version of the model that produces the best VSFS spectra. Calculated VSFS spectra elucidate the specific molecular origins of peaks in experimental spectra, including information about conformation, orientation, and vibrational mode nature. This provides a direct link between experimental measurements and theoretical calculations that provide specific molecular behavior that may not be probed experimentally.

Going organic: Modeling the vibrational sum-frequency spectra of atmospherically important organics at the vapor/water interface

246th National Meeting (2013)

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