Laser Studies of Equilibrium and Time Dependent Processes at Liquid Interfaces

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9313778 Eisenthal In this project of the Physical Chemistry Program of the Chemistry Division, Prof. K.B. Eisenthal of Columbia University will investigate the properties of and processes on liquid interfaces using non-linear optical methods based on second harmonic and sum frequency generation techniques. The aim of this work is to obtain a molecular level description of equilibrium and time dependent processes at vapor/liquid, liquid/liquid, and liquid/solid interfaces. The equilibrium processes include chemical equilibria such as a new method for measuring acid-base equilibrium constants at interfaces, isomeric equilibria at interfaces of molecules that are known to be sensitive to polarity, and the investigation of charged molecules at liquid interfaces. Ultrafast photochemical and photophysical events such as photoisomerization at air/ liquid, liquid/liquid, and liquid/solid interfaces as well as the dynamics of solvation initiated by a large change in the molecular dipole moment following photoexcitation of interface molecules and other phenomena will be investigated. %%% Interfaces are the sharply delineated geometric boundaries that separate different media from one another. The chemical and physical processes that occur at interfaces differ from those that take place within either of the media. A common example is the bending of a light beam as it traverses the boundary between air and water. While moving along a straight line path in both media, air and water, the beam is bent at the boundary face. Other examples are the evaporation of a liquid, whereby individual molecules move across the boundary surface from the liquid to the vapor, and chemical processes on surfaces which differ from those that take place in the bulk medium. While these and other common interfacial processes are reasonably well understood on the basis of macroscopic, phenomenological theories, it is important to know on a molecular level of description how these come about. It is the purpose of this research project to investigate interfacial processes in such a way that they can be understood on the basis of interactions between molecules, and between molecules and electromagnetic radiation. Though this research will concern itself with fundamental, basic questions of the chemistry and physics of interfacial phenomena, it has relevance to major environmental issues of air/water, oil/ water, and soil (silicates)/water interfaces. ***