Soft interfaces such as ice or those containing multiple species are common in biology, the environment, and technological applications. Probing soft, complex interfaces, particularly when buried between two condensed phases, presents many challenges. The only method currently 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 nonunique. This problem has long been recognized by SFG practitioners; the solution is to measure the complex amplitude. Several methods for determining the amplitude have been devised. None produce an absolute measurement. This contribution reports a nonlinear interferometer, that not only addresses this complex measurement issue, but it also detects even low concentration interfacial species. This presentation will discuss amplitude measurements on burried ice interfaces.

Interactions at ice interfaces

ACS Fall 2021

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