Creation and Reaction of Solvated Electrons at and near the Surface of Water

Spiers Memorial Lecture: New directions in molecular scattering

The field of molecular scattering is reviewed as it pertains to gas-gas as well as gas-surface chemical reaction dynamics. We emphasize the importance of collaboration of experiment and theory, from which new directions of research are being pursued on increasingly complex problems. We review both experimental and theoretical advances that provide the modern toolbox available to molecular-scattering studies. We distinguish between two classes of work. The first involves simple systems and uses experiment to validate theory so that from the validated theory, one may learn far more than could ever be measured in the laboratory. The second class involves problems of great complexity that would be difficult or impossible to understand without a partnership of experiment and theory. Key topics covered in this review include crossed-beams reactive scattering and scattering at extremely low energies, where quantum effects dominate. They also include scattering from surfaces, reactive scattering and kinetics at surfaces, and scattering work done at liquid surfaces. The review closes with thoughts on future promising directions of research.

Spectroscopy and dynamics of the hydrated electron at the water/air interface

The hydrated electron, e-(aq), has attracted much attention as a central species in radiation chemistry. However, much less is known about e-(aq) at the water/air surface, despite its fundamental role in electron transfer processes at interfaces. Using time-resolved electronic sum-frequency generation spectroscopy, the electronic spectrum of e-(aq) at the water/air interface and its dynamics are measured here, following photo-oxidation of the phenoxide anion. The spectral maximum agrees with that for bulk e-(aq) and shows that the orbital density resides predominantly within the aqueous phase, in agreement with supporting calculations. In contrast, the chemistry of the interfacial hydrated electron differs from that in bulk water, with e-(aq) diffusing into the bulk and leaving the phenoxyl radical at the surface. Our work resolves long-standing questions about e-(aq) at the water/air interface and highlights its potential role in chemistry at the ubiquitous aqueous interface.

Water as a sensor of weak impacts on biological systems

A characteristic feature of weak impacts is the non-monotonic response of living organisms and model biological systems to monotonically decreasing impacts. The qualitative similarity of the effects caused by the different acting factors makes one think about the common cause of the observed effects, which is water. A comprehensive analysis of the actual composition of water indicates that water under normal conditions is a multicomponent open non-equilibrium system. Nanobubbles that are always present in water play a significant role in the properties of dilute aqueous solutions. When collapsed, they can produce active oxygen and nitrogen species that have a strong effect on biological systems. Significant non-monotonic changes in electrical conductivity found in a series of sequentially diluted solutions subjected to vigorous shaking after each dilution convincingly demonstrate the presence of chemical changes in the composition of aqueous solutions explained by mechanochemical processes. Similar changes were observed in water samples prepared in the same manner with vigorous shaking and dilution without the addition of any chemical compounds. The long-term evolution of the conductivity of such solutions depends on the chemical structure of the solutes.