Observations on the Electronic Character of Anions and Cations near Water Liquid/Vapor Interfaces

In recent years, many researchers have become interested in chemical reactions, photon-induced processes, and other events taking place at or near aqueous liquid/vapor or ice/vapor interfaces. Such studies relate to a wide variety of atmospheric, oceanographic, and environmental issues. Near these interfaces, atomic and molecular anions and cations display quite different behaviors than when they are fully solvated in the bulk medium. When they exist near an interface, some cations capture an excess electron to produce new neutral-molecule electronic states. Some such cations can use an attached electron to assist in hydrolyzing one of their first-solvent-shell molecules. Anions residing near an interface are less solvent-stabilized than when in the bulk, causing their electron binding energies to decrease as they approach an interface, as a result of which their ability to act as reducing agents increases. Many multiply charged anions even become electronically metastable with respect to electron loss near an interface. Thus, for both cations and anions, it is important to develop tools for characterizing their varying electronic-state nature as they migrate between bulk solvation and liquid-vapor interface positioning.