Molecular Structure at Surfaces Through Spectroscopy and Simulations

Abstract:

Even-order nonlinear spectroscopies such as second harmonic (SHG) and sum frequency generation (SFG) are valued for their sensitivity to interfacial structure as they are capable of discriminating from adjacent bulk phases based on symmetry. Visible-infrared SFG spectroscopy additionally harnesses the sub-molecular structural probe of a vibrational spectroscopy by tuning the infrared laser over molecular resonances.  As a result, over the past two decades, SFG spectroscopy has been successfully applied to a wide variety of solid, liquid, and vapour interfaces, revealing signatures of the molecular organization that provide clues to the surface structure.  Our group has been working on techniques to assist in the molecular interpretation of the SFG response.  For small molecules, this includes grid computing-based searches to validate candidate orientation distributions based on the experimental data.  For larger molecules with additional conformational flexibility, we employ molecular dynamics simulations to further refine our efforts to interpret the SFG data.  Our most recent efforts explore the use of phase-resolved SFG spectra in order to develop more sensitive functions for scoring trial molecular orientation distributions.  Our goal is to develop tools that are scalable to molecules of arbitrary complexity.  This talk will provide some examples to illustrate our path towards this direction.