LIQUID INTERFACES

What I have tried to do in these few pages is to kindle further interest and activity in the study of the equilibrium and dynamic processes at liquid interfaces, in part by demonstrating the power of second harmonic and sum frequency spectroscopy to probe these ubiquitous and often elusive regions of matter. From the studies outlined in this Account we see that we can gain new fundamental information on the orientation of molecules, their energetics of adsorption, the changes in chemical equilibria at interfaces, and the effects of hydrogen bonding and solvation on the vibrational spectrum, as well as hydrogen bonding and solvation effects on the structure and unexpected phase transition of molecules at interfaces. When there are charged species at the interface, the resulting polarization of bulk water molecules can be investigated using these methods. The time-dependent phenomena including the kinetics of adsorption and desorption, the rotation of molecules in the anisotropic field of an interface, and the photochemistry of an excited-state isomerization can also be studied by SHG and SFG techniques. Besides the desire of scientists to probe the fundamental laws that govern the intersting world of interfaces, there is keen interest due to their important role in environmental, medical, and technology issues. These include the effects of pollutants on the abundant life processes that occur at the air/water interfaces of oceans, lakes, and rivers, as well as the impact of these air/water interfaces on the earth's weather and atmospheric chemistry. Similarly the aqueous/solid interface is crucial to our understanding the multitude of natural phenomena that occur in the soil as well as the development of new knowledge necessary to deal with the massive effects of pollution in our soils and ground waters. In my view the investigation of interfaces is in its earliest stages of development and, with the application of modern spectroscopic methods and theoretical modeling, great advances can be anticipated not only in the fundamental science but in its application to important world problems. © 1993, American Chemical Society. All rights reserved.