Probing Both Ice and Multicomponent Interfaces

Seminar | February 19 | 4-5 p.m. | 120 Latimer Hall

 Mary Jane Shultz, Department of Chemistry, Tufts University

 College of Chemistry

Soft interfaces such as ice or those containing multiple species are common in biology, the environment, and technological applications. Probing these, particularly when the interface is buried between two condensed phases presents many challenges. The only current method available to probe such interfaces with molecular specificity is the vibrational spectroscopy, sum frequency generation (SFG). At atmospheric pressure, ice forms a familiar hexagonal phase with an hexagonal prism crystal structure. Although the hexagonal basal face has been probed in numerous experiments, probes of the prism sides are rare. From catalysis, we know that minority faces can have an outsized impact on chemistry. Both the molecular configuration and the SFG spectra of these rare faces will be discussed. Ice spectroscopy demonstrates one of the limitations of SFG. SFG attains surface sensitivity due to its nonlinear nature, but that nonlinearity carries a price: separating overlapping signals is difficult, usually leading to nonunique separation. This problem has long been recognized by SFG practitioners and several methods for determining the complex components of the signal have been devised. None produce an absolute measurement of the complex signal. This contribution reports a nonlinear interferometer, that not only addresses this complex measurement issue, but also detects even low concentration interfacial species. The nonlinear interferometer has been demonstrated in both scanning and broadband SFG systems. Thin films and other interfaces will be discussed. Specifically, we show that the conformation of molecules in a hydrophobic interface are significantly altered by water in the film.

 Light refreshments will be served at 3:50 at The Coffee Lab, 510-643-0572